close

Вход

Забыли?

вход по аккаунту

?

The evolution of the mm. interossei in the primate hand

код для вставкиСкачать
The Evolution of the Mm. Interossei
in the Primate Hand
0. J. LEWIS
Department o f Anatomy, St. Bartholomew’s Hospital Medical College,
Charterhouse Square, London E.C.1
ABSTRACT
Various conflicting views relating to the phylogenetic history of the
interossei are reviewed. The primitive mammalian (marsupial) precursors of these
muscles are shown to present a bilaminar arrangement: a dorsal layer of four bipennate abductor muscles (inserting into a proximal phalanx) is overlaid ventrally by
a sheet of ten flexores breves, grouped in pairs, and inserting as wing tendons into
either side of the extensor aponeurosis of the corresponding digit. The homologues
of these muscles are identified in the hands of representative Primates including
Homo. The dorsal abductors become the dorsal interossei proper; the flexores breves
become the palmar interossei, which are therefore frequently more numerous than
the four found in man. Certain of the flexores breves show a tendency to merge with
those subjacent abductors with which they insert. Thus, the descriptive human dorsal
interossei are composite muscles resulting from the amalgamation of a flexor brevis
with a dorsal interosseous proper. Comparative morphology is shown to provide a
logical basis for the understanding of the extensor apparatus of the human fingers.
The interosseous muscles have long
presented morphologists with certain perplexing features. These palmar (or plantar) adductors and dorsal abductors are
characteristically grouped about the middle digit, but the axis of the primate hand
(or foot) varies among species and even
intraspecifically. It may be shifted to the
second or even the fourth digit. Any such
shift apparently requires a drastic reshuffling of the muscle insertions, contrary to
the usual principles of myological evolution. Moreover, the muscles vary numerically, some Primates having as many as
six, or even seven, in the palmar series.
The supernumerary ones, however, although part of the same palmar sheet as
the remainder, are so disposed as to act
as abductors, closely related to and reinforcing the normal dorsal abductors.
Any satisfactory phylogenetic hypothesis
must explain equally shifts in axis and
variations in number.
The various explanatory hypotheses proposed all derive essentially from Cunningham’s (1882) studies on the marsupial
hand and foot, which established the
primitive mammalian pattern of the intrinsic musculature (fig. 1A). Cunningham demonstrated the presence of a basic
trilaminar arrangement of digital muscles
consisting of a dorsal layer abducting
ANAT. REC., 153: 275-288
from the middle digit, an intermediate
layer of bicipital flexores breves with
metacarpal origins and insertions either
side of the corresponding digit, and a
superficial layer of four adductors (Mm.
contrahentes). He held that the human
condition could be derived from such an
arrangement by assuming that the dorsal
abductors become the dorsal interossei,
certain of the flexores breves become the
palmar interossei, the remainder disappearing (fig. l B ) , and the first only of
the contrahentes remains as the M. adductor pollicis.’ Cunningham’s view was
adopted by Thane (1892).
A second, widely held, hypothesis derives from the work of Ruge (1878) on
the development of the pedal interossei.
He claimed to have shown the development of both plantar and dorsal interossei from paired muscles lying initially
on the plantar aspects of the metatarsals
(in the position of Cunningham’s short
flexors), those bellies destined to become
dorsal interossei later reaching their definitive position by migration into the
intermetatarsal spaces. Windle ( 1883)
reported similar findings for the human
___.-
1 Cunningham had earlier (1878) supposed that
the contrahentes layer provided the palmar interossei,
a view he modified later. His critjcs (e.g., Campbell,
’39) have sometimes failed to conslder the later, more
plausible version.
275
276
0. J. LEWIS
Fig. 1 A diagrammatic representation of the various suggested theories on the evolution
of the Mm. interossei. A, the arrangement of the dorsal and intermediate muscle layers in
the primitive mammalian hand (the contrahentes layer is not shown); the four bipennate
dorsal abductor muscles are labelled Abl, Ab2, Ab3 and Ab4; the ten flexores breves are
stippled and indicated by Arabic numerals (the marginal members of this series, the first
and the tenth, are shown in darker stippling); the metacarpals are indicated by Roman
numerals. The shading conventions shown in A are retained in all other parts of the figure
and a muscular component which is believed to disappear is represented by a broken line,
as is the primitive site of a muscle which has undergone a supposed migration; the arrows
indicate the direction of such postulated movement. B, the view of Cunningham (1882).
C, the view of Windle (1883). D, the view of Forster (‘16). E, the view of McMurrich (‘03).
277
PRIMATE MM. INTEROSSEI
hand (fig. 1C). This hypothesis recognized no derivatives of Cunningham's dorsal abductor layer in the human hand
and was supported by Campbell ('39),
Keith ('48) and Haines ('50). Its attraction seems to be its provision of a facile
mechanism whereby to explain shifts in
the palmar or plantar axis, the axis becoming dependent solely upon which individual muscles undertake the dorsal
migration.
A third hypothesis interprets the dorsal
interossei as composite muscles, resulting
from the amalgamation of a dorsal abductor with a short flexor - in each case one
of those short flexors which Cunningham
supposed to have disappeared (fig. 1D).
This view received support from a detailed comparative study by Forster ('16)
and was deemed helpful by Bunnell ('42)
and by Eyler and Markee ('54) in elucidating the human condition. Earlier a
somewhat similar view was proposed by
McMurrich ( ' 0 3 ) , modified, however, by
his rather unorthodox views upon the
phylogeny of the thenar and hypothenar
musculature. Most morphologists believe
that the marginal members of the flexor
brevis series (the first and tenth) have,
as their human homologues, the M.flexor
brevis pollicis and the deep portion of the
M. opponens minimi digiti ( St. John
Brooks, 1886); McMurrich, however, believed that the thenar and hypothenar
muscle groups are entirely derived from
the primitive tetrapod flexor brevis superficialis. Inherent in this conception is the
difficulty of having to account for all ten
of the short flexors in the remainder of
the palm. McMurrich's solution, summarized in figure lE, postulated that the
first and tenth flexores breves have become the first and fourth human palmar
interossei, and that the first dorsal interosseous muscle, like the fourth, incorporates not one, but two flexores breves.
- RL
Fig. 2 The extensor apparatus of the human left ring finger (anularis). The terminology used is that of Landsmeer ('49, '55); alternative terms used by Haines ('51) are shown
in brackets. DB, deep belly (superficial belly) of fourth dorsal interosseous; DTL, deep
transverse ligament of palm; ET, extensor digitorum tendon; LI, lamina intertendinea; L3,
tendon of third lumbrical; PI, third palmar interosseous; PP, palmar pad (with the attachment of a slip of the metacarpophalangeal collateral ligament to its margin); PT, medial
tendon (phalangeal tendon) cut short of its insertion to the proximal phalanx; RL, oblique
band of retinacular ligament (link ligament); SB, superficial belly (deep belly) of fourth
dorsal interosseous; TL, transverse lamina (deep layer of hood ligament); WT, wing tendon
(side slips).
278
0. J. LEWIS
This involves the supposition that in each
case one of these two short flexors has
transferred its insertion across an interdigital cleft.
Phylogenetic considerations apart, renewed interest has recently developed in
the insertions of the Mm. interossei in
man, and in the detailed anatomy and
function of the digital extensor apparatus,
in consequence of which a much more
precise knowledge of the human arrangement has emerged. Figure 2 is taken from
a dissection performed with the hindsight
provided by the work of Bunnell (’42),
Braithwaite, Channell, Moore and Whillis
(’48), Landsmeer (’49, ’55) and Haines
(’51). Certain minor details have been
omitted from this diagram : thus, Haines
(’51 ) described an additional thin superficial layer to the hood, and Landsmeer
(’49) described the retinacular ligament
as having an additional transverse band.
It is clear that, usually, a dorsal interosseous muscle divides into two bellies, the
more dorsal belly inserting on the proximal phalanx and the more ventral furnishing a tendon which crosses more
superficially to a dorsal insertion into the
extensor expansion. As Salsbury (’37)
first pointed out, however, the relative
contributions to these two insertions vary
with the different dorsal interossei: the
first inserts solely into the proximal phalanx; the other three insert additionally
into the extensor expansion, the phalangeal insertion being greatest for the second, least for the third, and intermediate
for the fourth. Landsmeer (’55) moreover showed that the tendon of the dorsal
belly reaches its phalangeal insertion by
passing deep to the transverse lamina,
whilst the tendon of the ventral belly
passes superficial thereto to attain the
extensor expansion. He also showed that
the first dorsal interosseous may also have
a ventral belly inserting into the transverse lamina or even into the wing of the
extensor expansion. Various authors (Forster, ’16; Salsbury, ’37; Landsmeer, ’55)
have stressed that the palmar interossei
(like the ventral bellies of the dorsal interossei) are inserted entirely into the extensor expansion, reaching it by passing
superficial to the transverse lamina - yet
nevertheless many textbooks still describe
a partial phalangeal insertion as the normal arrangement. The interesting generalization which emerges from these considerations is that the extensor apparatus
of each finger displays symmetrically disposed wing tendons, derived either from
a palmar interosseous or from the ventral
belly of a dorsal interosseous (and reinforced on the radial side by a lumbrical).
The division of the dorsal interosseous
muscle into dorsal and ventral bellies is
interpreted (Salsbury, ’37; Haines, ’51;
Landsmeer, ’55) as a functional modification related to the different insertions and
actions of the two bellies - the phalangeal tendons acting on the metacarpophalangeal joints, the wing tendons acting on the inter-phalangeal joints, as
described by Stack (’62, ’63). These descriptive findings lack that basis of understanding which comparative morphology
often provides. Yet there are many features suggestive of a common basic primate plan.
As already noted, it is universally accepted (fig. 1 ) that the human palmar
interossei are derived from Cunningham’s
intermediate palmar layer of short flexors.
There can also be little doubt that the
supernumerary so-called palmar interossei, found in many other Primates, are of
similar derivation. Henceforth in this
paper all these muscular units in subhuman Primates will be referred to as
Mm.flexores breves (and the individual
bellies will be identified by reference to
the numbering in fig. 1 ) ; this nomenclature is preferable to “palmar interosseous,” since this latter term, borrowed
from human anatomy, carries with it
functional implications and notions of homology not applicable throughout the primate series. In this context it must be
significant that the human dorsal interossei are double-bellied, each belly - dorsal or ventral - having a characteristic
mode of insertion. It is herein suggested
2Note how Landsmeer (’55) and. Haines (’51) described these bellies as “superficial” and “deep”;
confusingly, however, they used these terms in opposite senses, the one author considering arrangements
from a dorsal viewpomt, the other from the palmar
aspect.
3 They should perhaps more properly be called Mm.
flexores breves profundi, the term applied to their
homologues in the amphibian and reptlle hand. These
lower tetrapods also present a flexor brevis medius
and superficialis, represented i n the mammalian hand
by the more superficial muscle and tendon layers.
279
PRIMATE MM. INTEROSSEI
that in fact the human dorsal interossei
are composite muscles derived from one
of the primitive two-headed dorsal abductors with a phalangeal insertion, compounded with a flexor brevis, and it will
be shown that a detailed analysis of the
insertions in relationship to the digital
extensor apparatus in man and other Primates is wholly confirmatory of this conclusion.
OBSERVATIONS
Trichosurus vulpecula
This species shows a close approximation to the basic mammalian arrangement
described by Cunningham and illustrated
schematically in figure 1A. The four bipennate abductor muscles of the dorsal
layer are orientated about the middle
digit, and are overlaid ventrally by the
sheet of flexores breves. The marginal
members of this latter layer, being comMATERIAL AND METHODS
ponents of the thenar and hypothenar
The present hypothesis is obviously groups, are beyond the scope of this disstrengthened if it can be shown that in cussion; thus eight muscles (numbers two
the primitive (marsupial) condition the to nine in fig. 1) remain for consideration.
digital dorsal abductors have a proximal The first of these is related to the ulnar
phalangeal insertion whilst the flexores side of the first metacarpal, the last to
breves of the intermediate layer insert the radial side of the fifth metacarpal.
into the extensor expansion. The classical The remainder are grouped in three pairs
literature affords no information on this arising from the central three metacarpoint but implies that the muscles of both pals. It is preferable here to speak of
layers insert into the phalanx or into a pairs of individual muscles rather than to
metacarpo-phalangeal sesamoid. This ap- adopt the customary designation of single
bicipital muscles, since the individual
parent detail, which however has signifi- members of each pair are, in fact, encance in the present context, was re- tirely separate entities.
examined by a dissection of the hands of
The tendons of the dorsal abductors
the common brush-tailed possum (Tri- merge with the surfaces of the metacarpochosurus vulpecula) and the Virginian phalangeal joint capsules and insert into
opossum (Didelphys marsupialis).
the bases of the proximal phalanges. The
The interossei were carefully dissected tendons of the flexores breves pass to a
in the hands of the following primate spe- more dorsal insertion and are totally atcies: chimpanzee ( P a n satyrus), white- tached to the margins of the correspondnosed monkey (Cercopithecus nictitans), ing extensor tendons (not the base of the
weeper capuchin monkey (Cebus nigrivit- phalanx as hitherto described) here formtutus) and white-thighed colobus monkey ing wing tendons. The wings of the extensor apparatus are not, therefore,
(Colobus polyhomos vellerosus).
The Mm.interossei were dissected in 25 uniquely human characteristics but anhuman hands, particular care being taken cient mammalian features. (Description
to determine the precise details of their of the contrahentes layer is irrelevant to
the present discussion. )
insertions and the relationship of these to
the digital extensor apparatus. The first
Didelphys marsupialis
palmar interosseous was exposed from the
The general muscle pattern reflects that
dorsal aspect by reflecting the radial head
described for Trichosurus but with some
of the first dorsal interosseous from its modification of the muscle insertions. The
origin on the first metacarpal. In many flexores breves are but partially continued
cases the insertions of the other interossei as wings to the extensor tendons, for, as
were most easily examined by longitudi- they skirt the metacarpo-phalangeal sesanally splitting the extensor digitorum ten- moids, they gain an attachment thereto.
don of the separated finger, and laying The fourth dorsal abductor muscle has a
either half (with its attached transverse double tendon of insertion, slips passing
lamina and wing tendon) away from the to both sides of the fourth interdigital
metacarpo-phalangeal joint .
cleft where they find insertion into the
280
0 . J. LEWIS
The pattern of insertion may best be
considered by first describing those situations where there are tendons of both a
dorsal interosseous and a flexor brevis,
e.g. the radial side of the medius (fig. 3 ) .
As in man, a strong transverse lamina
passes from each side of the extensor tendon to invest the metacarpo-phalangeal
joint and attach to the palmar ligament.
It constitutes a useful morphological landPan satyrus
mark. The tendon of the dorsal interosAmong the Primates this species may seous commences on the volar surface of
usefully be considered first, since the the muscle and the fully constituted tenmuscular components corresponding topo- don passes deep to the transverse lamina
graphically to the human interossei are to insert into the base of the proximal
here clearly defined and that blending of
adjacent muscle bellies which has occurred repeatedly in other Primates (and
even in members of other mammalian
orders) is here minimal.
There are four dorsal abductor muscles, similar in disposition to those in
marsupials, each arising from a pair of
adjoining metacarpals, and abducting
digits two, three and four from an axis
formed by the middle digit; these muscles
are usually called dorsal interossei. On
their palmar surface is a series of fusiform muscles, each arising from a single
metacarpal, and clearly homologous with
the flexores breves. Seven such are present, corresponding to numbers three to
nine inclusive in the primitive palm (fig.
1A); these are the muscles commonly
described as palmar interossei. Most
authors (Hepburn, 1892; Sonntag, ' 2 3 )
have recognized only six of these muscles,
failing to observe the most radial member of the series (number three) Forster
('16), however, recognized the full complement of seven in a specimen of Troglodytes niger. (In the present specimen
muscle number three was an entity clearly
separated from the underlying dorsal interosseous but perhaps, as will be shown
for the homologous muscle in man, there
is here individual variation.) Of these
muscles, numbers four, seven and nine
3 The muscles and extensor apparatus
correspond in position to the ulnar three onFig.
the radial side of the middle finger (medius)
human palmar interossei, and will be of the right hand of Pan satyrus. The radial head
shown to be homologous therewith: mus- of the second dorsal interosseous has been cut
cles three, five, six and eight are, how- from its origin on the second metacarpal; the
ever, intimately related, both at origin and flexor tendons and the second lumbrical muscle
are removed. DI, second dorsal interosseous; FB,
insertion, to the subjacent dorsal inter- flexor brevis; L2, tendon of the second lumbrical;
ossei.
other lettering as in figure 2.
contiguous sides of the proximal phalanges of the fourth and fifth digits. This
is a common, if not canonical, insertion
for this muscle in marsupials, and was
noted earlier by St. John Brooks (1886)
in Didelphys and Trichosurus (although
not observed in the present specimen of
Trichosurus vulpecula).
PRIMATE M M . INTEROSSEI
phalanx. The tendon of the flexor brevis
passes superficial to the transverse lamina
and is inserted entirely into the extensor
aponeurosis, forming its wing tendon, and
is joined here by the second lumbrical
tendon. Although the ventral flexor brevis
has the descriptively more dorsal insertion, its tendon does not cross over that
of the dorsal interosseous, owing to the
habitually flexed position of the metacarpo-phalangeal joint. This description
is also applicable to the insertions on the
ulnar side of the medius, the ulnar side
of the anularis and the radial side of the
index. In this last digit the separate identity of the flexor brevis is emphasized by
the well-marked aponeurotic surface of
the first dorsal interosseous; the flexor
brevis is represented proximally by a slender tendon of origin only, but its muscular belly extends far distally onto the
dorsal interosseous tendon, before giving
rise to a rather feeble tendon which inserts in the usual fashion as a wing
tendon.
On those sides of the digits lacking a
dorsal interosseous insertion - the ulnar
side of the index and the radial sides of
anularis and minimus - the arrangements are as shown in figure 3 , but with
the omission of the dorsal interosseous :
the flexor brevis (i.e. a palmar interosseous) passes superficial to the transverse
lamina to insert exclusively as the wing
tendon of the extensor apparatus. In the
specimen dissected there was no muscle
corresponding to the human first palmar
interosseous - number two of the flexor
brevis series. However in this situation
St. John Brooks (1887) described a fibrous
band in the chimpanzee and a muscular
belly in the orang and gibbon. All the
flexor brevis tendons, as they lie superficial to the transverse lamina, are invested by a thinner more superficial layer
of the hood. As noted above, a similar
thin superficial lamina of the hood ligament occurs in man.
The flexores breves have a fusiform
appearance in norma palmaris, often with
a small proximal tendon of origin attached to the metacarpal base: the deep
aspect of the fusiform belly, however,
gains appreciable origin from that ventral
part of the metacarpal shaft which is free
28 1
of dorsal interosseous attachment and an
intervening fibrous septum emphasizes
the separate identity of the two muscles.
The insertion of the fourth dorsal interosseous shows a departure from the general plan elaborated above, recalling the
common double insertion of the homologous marsupial muscle. In addition to
the usual abducting phalangeal tendon
passing deep to the transverse lamina on
the ulnar side of the anularis, a second
slender tendon arises from the aponeurotic palmar surface of the muscle, and
disappears beneath the transverse lamina
on the radial side of the minimus. This
latter tendon does not, however, reach
the base of the proximal phalanx here,
but gains final attachment to the metacarpal head.
Cercopithecus nictitans
In essentials the arrangement of the
intrinsic musculature is comparable to
that described for Pan, seven, discrete,
flexores breves, and four dorsal interossei
being present. Again the former insert by
wing tendons into the extensor aponeurosis and the latter by abducting tendons
into the bases of certain of the proximal
phalanges. (The fourth dorsal interosseous possesses only a single abducting tendon, the supernumerary chimpanzee tendon to the radial side of the minimus not
being elaborated here.) The transverse
lamina has not achieved the high degree
of differentiation observable in Pan, but
the more extended position of the metacarpo-phalangeal joints results in the dorsal interosseous tendons being crossed
superficially by those of the flexores
breves, as these proceed to their more
dorsal insertions.
Cebus nigrivittatus
The hand shows the usual four dorsal
abductors (dorsal interossei). There are,
however, eight members of the flexor
brevis series, seven occupying the same
locations as those in Pan and Cercopithecus, together with an additional one on
the ulnar side of the first metacarpal.
This last muscle belly, homologous with
the human first palmar interosseous, OCcurs (apparently variably) in other monkeys and has been noted by St. John
282
0.
J. LEWIS
Brooks (1887) in Cercopithecus, Macacus,
Pithecia and Hapale. Those four members of the flexor brevis series which are
homologous with the human palmar interossei (corresponding to numbers two,
four, seven and nine in fig. 1 ) all exhibit
a typical insertion as wings of the extensor aponeurosis. In this species the
transverse lamina is variably differentiated regionally, but where well-marked
it lies as usual deep to the palmar interosseous tendon. The bellies of the remaining flexores breves (numbers three, five,
six and eight) are somewhat merged with
the subjacent dorsal interossei. The tendons of insertion of the flexores breves
and the dorsal interossei on the radial
sides of index and medius show a mutual crossing similar to that noted in
Cercopithecus, as they pass to their respective insertions into the wings of the
extensor aponeurosis and the proximal
phalangeal bases. The insertions on the
ulnar sides of medius and anularis are,
however, modified but the mechanism of
the change here is unmistakably clear and
elucidates certain parallel human specializations. In each instance the partially
united bellies of the flexor brevis and the
dorsal interosseous give rise to their own
tendons which cross as usual alongside
the metacarpo-phalangeal joints : both
tendons, however, insert into the wing of
the aponeurosis, there being no phalangeal insertion. The tendon of the dorsal
interosseous has, in effect, relinquished
its phalangeal attachment and merged
with the deep aspect of the overlying
flexor brevis tendon, which thus carries
its insertion distally into the aponeurosis
wing. Such a process is, of course, a
common feature of myological evolution
elsewhere.
Colobus polyhonzos vellerosus
The usual four dorsal interossei are
present plus seven flexores breves, comparable to the seven described for Cercopithecus. The three flexores breves corresponding to the three ulnar human
palmar interossei (there is none corresponding to the first of man) insert as
usual by wing tendons into the extensor
aponeurosis. The transverse lamina is
poorly developed. The bellies of the re-
maining four flexores breves are even
more intimately merged with the related
dorsal interossei than in the preceding
species. Despite this, in each instance the
tendons of the two morphological components retain their separate identity and
cross each other as in other monkeys.
The basal simplicity of insertion noted in
Cercopithecus is not, however, here completely retained: on the radial side of the
index the flexor brevis wraps over the
tendon of the dorsal interosseous (as it
does in Pan and sometimes in Homo) but
does not attain the wing, the whole mass
inserting on the phalangeal base, and on
the ulnar side of the medius some of the
dorsal component is annexed by the flexor
brevis tendon, a very slender phalangeal
tendon being alone retained. On the radial side of the medius and the ulnar side
of the anularis the insertions are uncomplicated, with tendons crossing, as usual,
as they pass to their respective insertions
into the proximal phalangeal bases and
the extensor aponeurosis wings.
Homo
The human interossei fit easily into
the general pattern already described for
other Primates. Any apparent uniqueness
investing them is largely the result of a
traditional terminology which ascribes to
man no more than four palmar and four
dorsal interossei. The human specializations parallel those readily interpretable
trends already noted in certain of the
digits of other Primates, while the separate identities of the insertion tendons of
flexor brevis and dorsal interosseous components are emphasized, not only by their
typical mode of crossing to different insertions, but also by their relation to a
tough, clearly defined transverse lamina.
It must be emphasized that the transverse
lamina is not part of the metacarpophalangeal joint but, together with the
common extensor tendon, constitutes an
entirely separate mobile sleeve investing
the dorsum and sides of the joint. Its
movement is enhanced by large bursae
intervening between this extensor apparatus and the joint capsule. Besides the
well-known dorsal bursa (which may communicate with the joint cavity) there is
frequently a large bursa deep to the trans-
PRIMATE MM. INTEROSSEI
verse lamina on each side. Where only a
palmar interosseous inserts the lateral
bursa separates the transverse lamina
from the collateral ligament of the joint;
where a dorsal interosseous inserts the
bursa intervenes between the transverse
lamina and the subjacent phalangeal tendon, which in turn is usually separated
from the collateral ligament of the joint
by a second deep bursa. The presence of
these lateral bursae (apparently not
hitherto described) facilitates the clear
and unequivocal demonstration of anatomical arrangements in this region. In
the following account the number of
hands, of the 25 dissected, showing any
particular variant is indicated by the figures in brackets following the description.
The hand of man shows, beyond reasonable doubt, the same seven flexores
breves already observed in the other Primates; in addition, a first palmar interosseous (flexor brevis two) is usually separately identifiable. These flexores breves
present a characteristic gross appearance,
i.e. they are fusiform, have often a slender proximal tendon of origin from the
metacarpal base but arise also from the
metacarpal shaft, and certain of them
show a marked tendency to merge with
a related dorsal interosseous (cf. Colobus
p e l y k m o s vellerosus). Flexores breves
two, four, seven and nine, however, remain independent as the palmar interossei. Despite categorical statements to
the contrary in the literature, many textbooks persist in ascribing to the palmar
interossei a dual insertion, into both the
extensor aponeurosis and the proximal
phalangeal base. It is here confirmed
that, with certain reservations, the normal
insertion of a palmar interosseous is by a
wing tendon into the extensor aponeurosis. To reach this attachment the tendon
passes superficial to the transverse lamina, to which i t is firmly attached; an
attachment which may be mistaken for
a phalangeal insertion. In the case of the
fourth palmar interosseous, however (as
previously noted by Eyler and Markee,
'54), the deep aspect of the wing tendon,
just about the point where it is joined by
the fourth lumbrical, often [ 111 becomes
adherent to the underlying phalangeal
base. This is clearly a secondary attach-
283
ment and wholly different from the direct
primary insertion of the phalangeal tendon
of a dorsal interosseous. (Occasionally
there is a true phalangeal tendon on the
radial side of the minimus, which will be
considered with the fourth dorsal interosseous.) Theoretically, it might be expected
that the first palmar interosseous would
also retain an insertion as a wing tendon
and, in fact, its tendon does often [ 111 pass
completely superficial to a transverse lamina (here immediately dorsal to the metacarpo-phalangeal sesamoid) to reach the
ulnar wing of the pollicial extensor apparatus. Such an insertion has been noted before by St. John Brooks (1886) and by
Poirier and Charpy ('01). Most textbooks,
however, give the insertion as the sesamoid
and base of the proximal phalanx; in this
present series the muscle was completely
arrested at the sesamoid in only four cases
but more often [ 8 ] was attached to sesamoid and wing jointly. Sometimes [2] the
muscle is not distinguishable from the
M. adductor obliquus which may then furnish the wing tendon.
The descriptive human dorsal interossei
are clearly composite muscles derived
each from a dorsal interosseous proper
(comparable to those of e.g. P a n ) together with a flexor brevis (numbers
three, five, six and eight). The second
dorsal interosseous exhibits this derivation in almost unmodified form, arrangements being virtually identical with those
described for this region of the hand in
P a n (fig. 2). There is variable fusion of
the muscle bellies of the flexor brevis and
the dorsal abductor (which may, however, remain separate) but their tendons
retain complete individuality as they pass
respectively superficial and deep to the
transverse lamina to reach their appropriate insertions into the wing of the
aponeurosis and the proximal phalangeal
base. Similar features are usually shown
by the fourth dorsal interosseous, where
the component bellies are again varipbly
fused and the flexor brevis is occasionally
almost independent. The tendons show
the usual insertions but part of the substance of the dorsal abductor may sometimes [4] accompany the flexor brevis
tendon superficial to the transverse lamina
and into the wing of the extensor aponeu-
284
0. J. LEWIS
rosis, resulting in a diminution in the size
of the phalangeal tendon. In one instance
the whole of the dorsal abductor was thus
inserted, there being no phalangeal tendon.
In one further instance the dorsal abductor tendon passed as usual deep to the
transverse lamina, but had lost its phalangeal insertion and gained instead an attachment to the deep aspect of the wing
tendon. Such modifications, exceptional
for the fourth dorsal interosseous, become
the rule for the third. The component
bellies of this third dorsal interosseous may
occasionally be clearly differentiated but
are most commonly inseparably fused : the
tendons, however, again clearly indicate
the muscle's phylogeny. Invariably a welldefined tendon passes superficial to the
transverse lamina to join the wing of the
aponeurosis. Rarely [2] a slender phalangeal tendon passes deep to the transverse
lamina to insert upon the proximal phalanx. Sometimes [6] a tendon similarly
passes deep to the transverse lamina but
then joins the deep aspect of the wing
tendon : in one such example such a tendon
was separated from the transverse lamina
by a bursa and retained a slender phalangeal insertion, emphasizing its derivation
from the dorsal abductor component. Generally [ 171 however, the whole of the third
dorsal interosseous inserts into the extensor aponeurosis by passing superficial to
the transverse lamina.
The constitution of the first dorsal
interosseous is especially informative. It
is a matter of commonplace dissecting
room observation that a volar portion of
this muscle, arising from the second metacarpal, wraps over the thick, phalangeal
tendon of the remainder, in its passage to
a more dorsal insertion. The dorsal part
of the muscle, arising from first and
second metacarpals and furnishing the
phalangeal tendon, has long been known
as the M. abductor indicis of Albinus
(1734) and the volar portion as the M.
interosseous prior indicis of Albinus (or
M. flexor brevis indicis or M. extensor
tertii internodii indicis of Douglas, 1750)
(Henle, 1855; Wood, 1866, 1867, 1868;
Le Double, 1897; Wood Jones, '49). This
arrangement clearly recalls that seen in
the comparable situation in Pun and in
Colobus polyhomos vellerosus. Again the
dorsal bipennate portion clearly represents the dorsal interosseous proper, and
terminates as the usual thick phalangeal
tendon gaining its insertion by passage
deep to the transverse lamina, where the
typical superficial and deep bursae may
invest it. The volar portion (flexor brevis
three) is variably separate and crosses
the phalangeal tendon with a variant degree of obliquity, to reach the surface of
the transverse lamina with which it
merges. It may be prolonged [ l ] into the
wing tendon (here mainly formed by the
large first lumbrical), it may terminate as
an abortive wing tendon adherent to the
shaft of the proximal phalanx [4] but most
frequently it simply merges into the transverse lamina [20]. The common statement
that the first dorsal interosseous inserts
into bone only is clearly an oversimplification of the facts.
The human dorsal interossei are thus
generally comparable in arrangement
with those of other Primates. One feature
appears, however, to obscure their basic
symmetrical pattern, the occasional occurrence [7] of a tendon on the radial side of
the minimus, passing deep to the transverse lamina, whose muscle of origin attaches to the fifth metacarpal shaft between the origins of the ulnar head of the
fourth dorsal interosseous and the fourth
palmar interosseous, and which is, effectively, a delamination of the former. The
tendon has the typical topographical relationships of the phalangeal tendon of a
dorsal interosseous; it typically [5] inserts
into the base of the proximal phalanx but
may fail to reach this and so terminate on
the metacarpo-phalangeal joint capsule
[2]. It is doubtless homologous with the
fibrous band noted in the same situation
in Pun, and with the common additional
insertion into the fifth digit shown by the
marsupial fourth dorsal interosseous; it is
PRIMATE MM. INTEROSSEI
probable that the bifid marsupial insertion
of this muscle represents the primitive condition.
CONCLUSIONS
Clearly there obtains a basic plan of
digital muscle architecture, equally applicable to man and to other Primates, which
reaches its clearest expression when the
transverse lamina is well developed, as in
Pan and Homo. (The essentials of this
arrangement are shown in fig. 2.) This
basic pattern may be masked by partial
fusion of the muscular bellies of certain
of the flexores breves with those of the
dorsal abductors with which they insert.
Modifications of insertion also occur, but
these specializations follow certain clearly
defined trends, and have apparently occurred independently and repeatedly
among the Primates. Thus, the prolongation of the flexor brevis into the wing
tendon may be attenuated, leaving the
muscle inserted into the transverse lamina; a dorsal interosseous phalangeal tendon, distal to its passage deep to the transverse lamina, may become incorporated
with the deep aspect of the corresponding
wing tendon, leading to diminution (or
even abolition) of its primary phalangeal
insertion; the dorsal abductor muscle may
even merge completely with its related
flexor brevis and the composite whole
give rise only to a tendon passing superficial to the transverse lamina into the
extensor aponeurosis wing. Examples of
these various specializations have been
described above in different Primates. It
is thus apparent that the recorded numerical variations of the primate Mm. interossei depend on terminological, rather
than morphological, considerations. The
specializations noted above also clarify the
mechanism by which the functional axis
of the hand may become changed. Thus,
if the belly of the second dorsal abductor
(fig. 1 ) should fuse, not with flexor brevis
five, but with the fourth muscle (whose
tendon then comes to form its sole insertion) the palmar axis becomes shifted
from the third to the second digit. A true
285
interpretation of the phylogenetic history
of the human muscular arrangements can
alone bring order and clarity to an otherwise complex and confused subject. The
findings for the human hand in this study
accord with Haines’ (’51) description of
the general anatomy of the extensor apparatus and they confirm and extend
Landsmeer’s (’55) findings regarding specific insertion details in the several fingers.
Although strictly beyond the scope of
the present account, it is noteworthy that
arrangements on the ulnar side of the
minimus accord with the basic finger pattern herein described. The superficial part
of M. abductor digiti minimi inserts into
the ulnar wing of the extensor aponeurosis; but, additionally, in every hand examined in the present series, a rounded
and separate tendon was found to emerge
from the core of the muscle (often from
a distinctly separate belly) and to pass
deep to the transverse lamina to a bony
insertion into the base of the proximal
phalanx. The M. abductor digiti minimi
is thus fully comparable to any typical
composite human dorsal interosseous (e.g.
the second). This arrangement, apparently not previously described, seems to
demand some revision of St. John Brooks’
(1886) classical account of the homologies of the hypothenar muscles.
Acceptance of the view developed herein implies rejection of the alternative earlier and conflicting phylogenetic theories
(fig. l ) , the foundations of which warrant scrutiny anew. Canonical terminology
recognizes only four representatives of the
primitive flexores breves - the four palmar interossei - in the human hand, and
no homologues of the flexores breves are
traditionally described as inserting with
the dorsal interossei. Cunningham ( 1882)
therefore theorized that the flexores breves
which formerly occupied these latter situations must have disappeared; as has been
shown, closer morphological analysis of
the human dorsal interossei shows this
view to be unfounded.
The view postulating dorsal migration
of certain of the flexores breves to become
286
0. J. LEWIS
dorsal interossei was based solely on the
interpretation of certain embryological
findings, at a time when inflexible views
on ontogenetic recapitulation prevailed.
Ruge (1878) and Windle (1883) were
thus seeking evidence of an ontogenetic
migration of the future dorsal interossei,
which they believed they had observed.
Re-examination of their illustrations, however, makes it apparent that no actual
migration occurs but instead a relative delay in the full development of the intermetacarpal parts of the dorsal interossei a delay associated with the later broadening of the hand and concomitant widening of the intermetacarpal spaces.
McMurrich's ('03) view that two flexores breves are incorporated with each of
the first and fourth dorsal interossei receives no support from human or comparative anatomy. Indeed, his figure of a
section from the hand of a 6 cm human
embryo appears amply to confirm the view
herein proposed, namely, that each human dorsal interosseous results from the
partial incorporation of a single flexor
brevis with a dorsal abductor muscle, and
that each palmar interosseous is a virtually unmodified flexor brevis. The observations made during this present study
and the factual data recorded in the literature (although not necessarily their interpretation) lead in escapably to this conclusion.
ACKNOWLEDGMENTS
I should like to thank Professor A. J. E.
Cave for providing the material used in
this study and for valuable advice in the
preparation of the manuscript.
LITERATURE CITED
Albinus, B. S. 1734 Historia Musculorum Ho.
minis. Haak and Mulhovium, Leyden.
Braithwaite, F., G. D. Channell, F. T. Moore and
J. Whillis 1948 The applied anatomy of the
lumbrical and interosseous muscles of the hand.
Guy's Hosp. Rep., 97: 185-195.
Bunnell, S. 1942 Surgery of the intrinsic muscles of the hand other than those producing
opposition of the thumb. J. Bone Jt. Surg.,
24: 1-31.
Campbell, B. 1939 The comparative anatomy
of the dorsal interosseous muscles. Anat. Rec.,
73: 115-125.
Cunningham, D. J. 1878 The intrinsic muscles of the hand of the thylacine (Thylacinus
cynocephalus), cuscus (Phalangista maculata)
and phascogale (Phascogale calura). J. Anat.
Lond., 12: 434-444.
-1882 Report on some points i n the
anatomy of the thylacine (Thylacinus cynocephalus), cuscus (Phalangista maculata) and
phascogale (Phascogale calura) collected during the voyage of H.M.S. Challenger in the
years 1873-1876; with a n account of the comparative anatomy of the intrinsic muscles and
nerves of the mammalian pes. Challenger
Reports, 5: 1-192.
Douglas, J. 1750 Myographiae Comparatae.
Kincaid and Crawfurd, Edinburgh.
Eyler, D. L., and J. E. Markee 1954 The anatomy and function of the intrinsic musculature
of the fingers. J. Bone Jt. Surg., 36A: 1-9.
Forster, A. 1916 Die Mm. contrahentes und
interossei manus in der Saugetierreihe und
beim Menschen. Arch. Anat. Physiol., Lpz.,
1916: 101-378.
Haines, R. W. 1950 The flexor muscles of the
forearm and hand in lizards and mammals.
J. Anat. Lond., 84: 13-29.
1951 The extensor apparatus of the
finger. J. Anat. Lond., 85: 251-259.
Henle, J. 1855 Handbuch der Systematischen
Anatomie des Menschen. Erster Band. F.
Vieweg und Sohn, Braunschweig.
Hepburn, D. 1892 The comparative anatomy
of the muscles and nerves of the superior and
inferior extremities of the anthropoid apes.
Part I. J. Anat. Lond., 26: 149-185.
Keith, A. 1948 Human Embryology and Morphology, sixth edition, Edward Arnold, London.
Landsmeer, J. M. F. 1949 The anatomy of the
dorsal aponeurosis of the human finger and
its functional significance. Anat. Rec., 104:
31-44.
1955 Anatomical and functional investigations on the articulation of the human
fingers. Acta Anat. Suppl. 24.
Le Double, A. F. 1897 Trait6 des Variations du
Syst&me musculaire le l'homme. Schleicher
Frbres, Paris.
McMurrich, J. P. 1903 The phylogeny of the
palmar musculature. Am. J. Anat., 2: 463500.
Poirier, P., and A. Charpy 1901 Trait6 d'Anatomie Humaine. Tome 11. Masson et Cie, Paris.
Ruge, G. 1878 Entwicklungsvorgange a n der
Muskulatur des menschlichen Fusses. Morph.
Jb., 4 (Suppl.): 117-152.
St. John Brooks, H. 1886 On the morphology
of the intrinsic muscles of the little finger,
with some observations on the ulnar head of
the short flexor of the thumb. J. Anat. Lond.,
20: 645-661.
1887 On the short muscles of the pollex and hallux of the anthropoid apes, with
special reference to the opponens hallucis. J
Anat. Lond., 22: 78-95.
Salsbury, C. R. 1937 The interosseous muscles
of the hand. J. Anat. Lond., 71: 395403.
Sonntag, C. F. 1923 On the anatomy, physiology and pathology of the chimpanzee. Proc.
zool. SOC.Lond., I: 323-429.
Stack, H. G. 1962 Muscle function i n the
fingers. J. Bone Jt. Surg., 44B: 899-909.
PRIMATE MM. INTER0 S SEI
1963 A study of muscle function in the
h g e r s . Ann. roy. Coll. Surg. Engl., 33: 307-322.
Thane, G. D. 1892 Quain’s Elements of Anatomy. Ed. by. E. A. Schafer and G . D. Thane.
Vol. 11, pt. 2, 10th ed. Longmans, Green and
Co., London.
Windle, B. C. A. 1883 On the embryology of
the mammalian muscular system. No. I - the
short muscles of the human hand. Trans. R.
Irish Acad., 28: 211-240.
Wood, J. 1866 Variations in human myology
observed during the winter sesson of 1865-66
287
a t King’s College, London. Proc. roy. SOC., 15:
229-244.
1867 Variations i n human myology observed during the winter session of 1866-67 a t
King’s College, London. Proc. roy. SOC., 15:
518-546.
1868 Variations in human myology
observed during the winter session of 1867-68
a t King’s College, London. Proc. roy. SOC.,16:
483-525.
Wood Jones, F. 1949 The Principles of Anatomy as Seen i n the Hand. BailliBre, Tindall
and Cox, London.
Документ
Категория
Без категории
Просмотров
2
Размер файла
1 130 Кб
Теги
primate, hands, evolution, interossei
1/--страниц
Пожаловаться на содержимое документа