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The anatomy of polydactylism in cats with observations on genetic control.

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The Anatomy of Polydactylism in Cats wj.th
Observations on Genetic Control
V. A. CHAPMAN AND FRED N. ZEINER
Department of Zoology, University of Denver, Denver, Colorado
Polydactylism is seen often enough that
both anatomists and geneticists have given
it their attention. Unfortunately, anatomical descriptions of isolated cases contribute little to an understanding of the hereditary basis. Geneticists have concluded
that polydactyly in the cat is produced by a
dominant gene with variable expressivity,
but the lack of precise anatomical description in many of their papers prevents identification of factors that might cause variation in expression of the trait.
In this work an attempt has been made
to correlate detailed descriptions of some
of the forms which polydactyly takes with
possible causes of variable expressivity.
Thirty-one cats have been used. The
genetic data support the idea of dominant
inheritance in general, but they also show
the need of considering each type of polydactyly separately from the standpoint of
controlling factors involved in variable expressivity. The types of polydactylism
available to the authors are described in
detail. Many other types have been reported. Howe (’02) gives a detailed description of a type not seen in this work.
The complete descriptions of several types
by Danforth (’47) include some types quite
similar to those here reported.
MATERIALS AND METHODS
Two cats of different polydactylous types
(no. 1000 and no. 300), each having one
normal parent, were mated. The male
(no. 1000) was also mated three times to
a normal female (no. 200) having no
history of polydactylism, and to a polydactylous female (no. 1203) of the first
litter of no. 1000 X no. 200. Photographs
were taken of both dorsal and ventral
aspects of all feet of polydactylous animals
to show the external configuration of the
duplication and x-rays were taken for
skeletal configuration. Fore- and hind legs
of one cat of each polydactyl type were
dissected to study musculature in particular, with less detailed observations being
made on innervation and vasculature.
For a description of normal cat anatomy
see Reighard and Jennings (’35). Figures
1, 4, 9, and 14 will aid visualization. For
ease of presentation, the term “digit” is
used to include the associated metacarpal
or metatarsal a s well as the phalanges.
Eight abnormal types of paws have been
found if all structures are considered.
Some types are identical in certain of their
features and IlLfferent in others. Three
types of fore-fee t (Types A-C) and 5 of hind
feet (Types D-H) will be described.
Skeletal anatomy. Types A and C were
identical except in pad configuration. Here
the carpus was normal, but the first digit
was duplicated. Rather than a single normal second digit, three normalIy appearing
digits extended from the trapezoid, each
having a metacarpal and three phalanges.
The medial of the two duplicated digits
articulated with the medial two-thirds of
the distal portion of the trapezoid, as did
the normal second digit. The lateral first
digit articulated with the lateral portion of
the trapezoid and with the most medial extremity of the unciform. The third, 4th,
and 5th digits were normal in so far as the
skeleton was concerned (fig. 2). Type B
differed from A, or C in that the medial
second digit had a “Y” at the distal end of
the proximal phalanx. The distal ends of
this peculiar phalanx each bore a normal
middle and then a terminal phalanx
(fig. 3).
Types D and H were comparable to type
A in that there were 5 metatarsals. Each
metatarsal bore three phalanges. Two full
Present address: Zoology Department, Indi.
ana University, Bl.oomington.
205
206
V. A. CHAPMAN A N D FRED N. ZEINER
digits articulated with the intermediate
cuneiform. This Fact and the general position of the digits indicated they represented
a duplication of the second digit. The
tarsus was normal (fig. 5). Type E was
comparable to type B of the fore-foot. This
type had all the duplications and omissions
that types D and F had and, in addition,
the medial second digit had a duplication
in the proximal phalanx in the form of a
"Y." As was seen in type B, the " Y bore
a middle and distal phalanx (fig. 6). Type
F differed from type E in that the " Y
duplication occurred in the metatarsal of
the lateral of the duplicated second digits,
rather than in the first phalanx of the
medial digit. The distal ends of the Yshaped metatarsal had the normal three
phalanges (fig. 7). Type G had the same
omissions and duplications of types D and
H, but in addition, two complete digits
articulated with the lateral cuneiform. This
indicates a duplication of the 4th digit.
There were 6 complete digits (fig. 8). Side
of claw retraction has sometimes been
used as a means of telling which specific
normal digit has produced a duplication
(Danforth, '47). Our data on this point
were insufficient to permit conclusions.
The Ossification centers of the metacarpals and metatarsals and their phalanges
develop before those of the carpus or tarsus
(Arey, '54). Each of these develops from
an individual ossification center. Probably
the force causing duplication acts before
the ossification centers of the tarsals and
carpals have appeared. Thus, no duplication of tarsal or carpal elements was found.
It is probable in partial or complete duplication of digits that a genetic mechanism
causes the appropriate ossification centers
to split. The work of Scott ('37) on salamanders supports this.
Examples of human polydactylism
closely resembling those seen in the cat
have been reported. Acker ('31) and
Snedecor and Harryman ('40) found cases
much like types A, D, and G . Horwitz ('40)
described a Y-shaped 4th metacarpal.
Cooperman ('30), Corrigan ('28), Penhallow ('28), and Zweig ('38) have mentioned a duplication of the second digit;
however, in these cases the thumb or the
hallux was present. Mitchell ('28),
O'Rahilly ('46), and Pekorny ('33) dealt
with duplications of the first digit. The
similarity of duplications in cat and human raises the possibility of related control mechanisms. It would be desirable to
have detailed anatomical studies in many
other species.
Musculature. In types A and C the
origin of the extensor carpi radizlis longus
was normal. As the tendon passed through
the radial side of the dorsal surface of the
distal end of the radius, instead of continuing on to its insertion, it split into two. parts.
Both of these tendons crossed the carpus
and one inserted into the dorsal surface of
the base of the medial second metacarpal,
although the other inserted on the dorsal
surface of the base of the lateral second
metacarpal. The extensor digitorum communis was normal from origin to a point
midway of the second metacarpal, already
having split into the 4 normal tendons. At
this point the most medial tendon inserted
at the base of the second phalanx of the
medial second digit while the other tendon
inserted at the second phalanx of the lateral second digit. The extensor indicus
was normal to the point of the base of the
radius where it divided into 4 tendons instead of the usual two. One ran to the
medial side of the medial second digit, the
second ran to the lateral dorsal side of the
medial second digit. The third tendon ran
to the medial side of the lateral second
digit and the 4th ran to the lateral side of
the lateral second digit. All 4 tendons inserted at the base of the second phalanx of
their respective digits. The extensor brevicis pollicis originated normally and passed
over the normal route until it reached the
proximal lateral point of the trapezoid,
where it inserted, rather than into the base
of the first metacarpal. The radial sesamoid of the carpus was incorporated in
this tendon as is normal. The flexor carpi
radialis was normal at its point of origin,
but did not insert in the third metacarpal.
Rather, it inserted at the base of the
medial second metacarpal and the base of
the second lateral metacarpal. The palmaris longus, also normal at origin, split
into 5 tendons. Each tendon gave off a
branch that spread into the multilobed pad
of the palm. The middle three of these
were traced to the integument covering the
pad. The tendons then inserted near the
ANATOMY AND GENETICS O F POLYDACTYLY
base of the first phalanx onto the outer
surface of the perforated portion of the
flexor sublimis tendon. They inserted on
each of the digits present, including both
of the duplicated second digits. The manner of insertion m s entirely normal. No
tendon was present that would indicate a
route going toward the first metacarpal.
The ulnar portion of the flexor sublimis
digitorum was normal. The radial portion
was normal in origin, but it then divided
jilt0 three slips, rather than the normal
two, and each gave rise to a tendon. The
two medial tendons passed to the lateral
and medial second digits and the lateral
tendon passed to the third digit. Manner
of insertion was normal. The 5 heads of
the flexor profundus digitorum were normal as was the convergence into a common
tendon. The common tendon divided into
the expected 5 tendons, each passing to
one of the digits. No extra tendon was
present which might be expected to pass
to the thumb. The insertions into the bases
of the terminal phalanges were normal.
There were 5 lumbricales present, rather
than the normal 4. The 5th lumbricalis
inserted on the radial side of the base of
the first phalanx of the second digit. The
abductor brevis pollicis, the flexor brevicis
pollicis, and the adductor pollicis of the
thumb were absent. The interossei of the
third, 4th and 5th metacarpals were normal. The origin of the flexor brevis digiti
secundi or the interossei of the second digit
was normal at the point of origin. Near its
distal end, instead of dividing into two
masses, it divided into 4. These passed
onto the lateral surfaces of the lateral and
medial second metacarpals. ‘They inserted
on the lateral surfaces of the base of the
first phalanx and its sesamoids, and partly
by slender tendons which were continued
dorsad to join the extensor tendon of these
digits. The abductor digiti secundi originated in three heads. Two were from the
radial and ventral surfaces of the bases of
the lateral and medial second metacarpals
and the third or normal head was from the
ventral surface of the trapezium. They inserted on the radial side of the base of the
first phalanx of the lateral and medial second digit and into its sesamoid. The adductor digiti secundi originated from a
single head from the ventral side of the
207
0s magnum in a normal manner. Very
shortly after the point of origin it split into
two masses, one of them going to the ulnar
side of the base of the first phalanx of the
medial second digit and the other inserted
into the ulnar side of the base of the first
phalanx of the lateral second digit.
The following muscles in type B were
identical to thost: described in type A: extensor carpi radialis longus, extensor indicus, extensor brevicis pollicis, flexor
carpi radialis, palmaris longus, both ulnar
and radial parts of flexor sublimis digitorum, lumbricales, interossei, flexor brevis
digiti secundi, arid adductor digiti secundi.
The extensor digiti communis originated
normally, but mjdway on the second metacarpal the most medial tendon split, one
part going to the medial second digit and
one to the laterd second digit. Thus far
it was like type A, but at the point of the
base of the most proximal phalanx of the
medial second digit, the tendon split again
and diverged to its insertion at the terminal phalanx of each phalangeal branch.
In the flexor profundus digitorum, the duplication was comparable to that of type
A up to the base of the most proximal
phalanx of the medial second digit. At
this point the tendon split again and inserted into the base of each of the terminal phalanges.
In types D and H the flexor longus digitorum was nornnal at its origin, but split
into 5 tendons rather than 4 at the middle
of the metatarsals. It inserted normally
into the terminal phalanges of all 5 digits.
The peroneus longus was normal to the
point of insertion, where it attached to the
base of the medial second metatarsal rather
than to the outer side of the base of the
first metatarsal. The extensor longus digitorum was norrnal from the point of origin
to the middle of the metatarsals. It had
already split into the usual 4 tendons and
the fibular three proceeded normally.
However, the mlost tibia1 of the 4 tendons
divided 1 cm clistad of the fibrous loop.
The divisions continued distad to the terminal phalanges of the lateral and medial
second digit. The tibialis anterior inserted
into the outer surface of the medial second
digit rather than into the first. The extensor brevis digitorum divided into 4
tendons, rather than three, with normal
208
V. A . C H A P M A N A N D FRED N. ZEINER
relationships otherwise. The flexor brevis
digitorum showed 5 instead of 4 slips and
they inserted into the base of the second
phalanx of each digit. The interossei of the
third, 4th, and 5th metatarsals were normal. The interossei of the second digit
paralleled the configuration of the interossei described in type A.
The peroneus longus, tibialis anterior,
extensor brevicis digitorum, and flexor
brevis digitorum had the same configuration in type E as has been described for type
D. The flexor longus digitorum in type E
split into 5 tendons at the middle of the
metatarsals. These proceeded distally on
the ulnar 4 digits and inserted on the terminal phalanges. The medial tendon went
distad to the level of the proximal phalanx
where it split into two tendons. Each of
the two proceeded distad over the duplicated two distal phalanges, where it inserted on the terminal phalanx. The extensor longus digitorum was also peculiar
to type E. It proceeded as described in type
D to the point of the proximal phalanx of
the medial second digit where the tendon
divided and paralleled the paired medial
and terminal phalanges, inserting on the
latter.
In type F the peroneus longus and the
tibialis anterior were like those in types D
and H. The flexor hallicus longus split at
the middle of the metatarsals into 5 tendons, as was seen in types D and H, rather
than into the normal 4, but 5 mm distad of
this division the second tendon from the
tibia1 side split again and sent a tendon to
each of the Y-shaped branches of the second metatarsal (fig. 5). Each of these in
turn went distally to insert into the base
of the terminal phalanx. The other 4
principal tendons corresponded to those of
D and H. A highly similar pattern of
subdivision to correspond with skeletal
changes was seen in the extensor digitorum longus, the extensor brevis digitorum, and the flexor brevis digitorum. The
interossei muscles of type F were the same
as in types D and H. The lateral division
of the Y-shaped second digit had no interossei muscles.
The flexor longus digitorum of type G
showed 6 tendons of insertion. The three
radial ones appeared as those described in
type D. The fibular second and third ten-
dons ran along the duplicated 4th digits to
insert on the terminal phalanges. The 6th
tendon inserted normally at the base of the
terminal phalanx of the 5th digit. The extensor longus digitorum, normally ending
in 4 slender tendons, terminated in 6 tendons in this type. The medial tendon duplication has been described i n types D
and H. The third tendon split again 1 cm
distad of the transverse ligament from
which it originated and each of these
paralleled one of the duplicated 4th metatarsals and their phalanges to insert on the
terminal phalanx of each. The extensor
brevis digitorum gave off 5 tendons, rather
than the usual three, and these then
showed normal relationships to the digits.
There were 8 lumbricales in contrast to
the 6 found in the normal. The 4 larger
ones had their origin from the outer surfaces of the expanded portion of the flexor
longus digitorum. Each ended in a slender
tendon which united with the divisions of
the tendons of the flexor brevis and the
united tendons passed to the 4 lateral digits. The other 4 had origin from the tendon of the flexor longus at the point where
it divided. Each occupied one of the 4
intervals between the 5 divisions and its
fibers originated from the proximal ends of
the two tendons that bounded its interval.
They inserted by a slender tendon into the
medial side of the third, the medial
4th and the lateral 4th metatarsals. At
the heads each divided and passed onto the
sides of its respective metatarsal. They
continued distad where they joined the extensor tendon near the distal end of the
first phalanx.
Muscle development depends upon the
development of cartilage and bone (Barth,
'53). Since bone and cartilage development precedes that of muscle, it is reasonable that the abnormal skeletal configurations previously described would produce
corresponding anomalies of musculature.
The serial homology which is seen in
the normal musculature of the fore-limb
and hind limb was paralleled in the abnormal cases here described. This is not surprising, since the skeletal duplication of
fore- and hind limbs is also comparable.
Innervation. The paws in all cases possessed normal functional ability and sensory reactions implying adequate innerva-
ANATOMY AND GENETICS OF POLYDACTYLY
tion. Additional branching of terminal
nerves to correspond with the digital duplications must have occurred. At the level
that such duplication would be expected to
occur, the nerves have already become embedded within the musculature or are SO
filamentous as to be extremely difficult to
follow. Hence, not all nerves have been
identified. Only those observed to deviate
will be described.
The superficial radial nerve of types A
and C ended in 7 branches as is normal.
Since there was no pollex, but rather a
duplicated second digit, it is possible that
the nerves of the pollex may have rotated
laterally to innervate the duplicated second
digit. However, since the nerves entered
typical second digit integument, it is more
probable that the two branches passing to
the pollex dropped out, and the two
branches that would normally go to the
second digit became duplicated. Distribution of the medial nerve was to all the
digits; probably it lost branches to the pollex and had duplications of other branches.
In types D, E, F, and H the medial
plantar nerve split into two parts as in the
normal animal, but the branch that would
have gone to a normal second digit split
again and sent filaments to both the lateral
and medial second digits. The superficial
peroneal nerve split into the normal 4
nerves which again divided, forming 8
filaments. The 6 lateral filaments went to
both sides of the three lateral digits. The
two medial filaments went to each of the
second digits. The more medial of the two
entered the medial side of the medial second digit, and the other branch entered the
lateral side of the lateral second digit. This
provides further indication that the duplication was of the second digit.
The medial plantar nerve of type G followed the pattern indicated above. The
superficial peroneal nerve differed in one
way from the description of previous types.
The branch supplying the 4th digit split to
send one filament to the medial side of
the medial 4th digit and one to the lateral
side of the lateral 4th digit.
Vasculature. Although vasculature was
studied, no discrete patterns were discernible in the various polydactyl types; hence,
no specific descriptions are given. This
finding is not surprising if the amount of
209
individual variation seen in normal paws
is considered. The report of Howe ('02)
also suggests that vasculature is a poor
criterion for the determination of causative mechanisms in polydactyly.
Pad configurirtion. O n the fore-foot,
the normal cat has a trilobed pad on the
palm, pads on the base of the middle
phalanx of each digit, and a pad at the
level of the carpus (fig. 9). The pads of
the hind foot are much the same except
that there is no pad at the level of the
tarsus (fig. 14). The hallux is vestigial in
the cat so no external pad is visible. Where
digits were duplicated, corresponding phalangeal pads were present. In some instances extra palm or sole pads were found.
In addition, certain individuals possessed
an extra digit that had no skeletal material associated with it.
In the fore-feet type A showed an extra
palm pad medially which in turn possesed
an integumental projection extending medially from it. The second digit was duplicated and the pollex was absent. Each
of the 5 digits showed a phalangeal pad
( f i g . 10). In type B 6 phalangeal pads
were present as well as an extra palm pad
which bore an integumental projection.
In the photograph (fig. 11) flexion of the
most medial digit brought the phalangeal
pad into apparent alignment with the
palmar pads. Five phalangeal pads were
present in type C. In addition, there was
an integumental digit protruding between
the medial and the lateral second digits.
This digit had neither bone nor muscle, but
it supported a claw (figs. 12, 13).
Turning to the hind feet type D had one
extra pad that was located on the second
duplicated digit (fig. 15). In type E, in
addition to an extra pad like that in D,
there was an extra sole pad on the tibial
side which in turn bore a small integumental projection (fig. 16). Six sets of
phalange were present in type F and each
bore a phalangeal pad (fig. 17). There
were 6 phalangeal pads and two extra sole
pads were found medially in type G (fig.
18). In type II the pad configuration was
like the fore-feet of type A, but in addition there was an integumental digit on the
tibial side which possesed no bone or musculature, but maintained a claw (figs. 19,
20).
210
V. A. CHAPMAN AND FRED N. ZEINER
TABLE 1
Anatomical type with relationship
A A A A A A
F F G G D D
1
A
D
2
1213 1214 1215
A A B E E A
G G DD DH
1216 1217
&fTb *;y*
K
D
!
1301 1302 1303 1304
A A N
DD
~~
N
*
DD
H H
12031 12032 12033 12034 12035 12036
N
A A
DD
A A
DD
A A
H H
A A
F G
N
N
* Polydactyl type of each foot, left and right forefeet above, left and right hind feet below.
N represents normal.
Genetic observations. One male cat
(no. 1000) fathered all the kittens of this
study and the results are given in table 1.
He was of types A and D (figs. 2, 5). He
had one normal and one polydactylous
parent.
He was crossed with a normal (no. 200)
to see if his specific type of polydactyly
would breed true. Three litters including
7 normal and 10 polydactylous kittens resulted. Three were identical with the
father, two were of types A and G, one
showed types A and F, one was of types B
and D, and the other three were even more
variable. One possessed types A, D, and
E and the other two showed types A, B, D,
and H. It should be noted that the latter
had no two feet alike. The results indicate that the specific phenotype of the
male did not breed true. However, the
basic pattern of the father persisted in all
of the polydactylous offspring. Scrutiny
of the other types shows them to be variations on a central theme. In addition it
should be noted that if an animal was
polydactylous, it was abnormal on all feet.
A female (no. 300) with types C and H,
whose mother had the same types and
whose father was normal, was mated with
no. 1000. Only one of the litter of 4 was
polydactyl. To be sure, it had the same
types as the father but, since it was a
ANATOMY AND GENETICS OF POLYDACTY’LY
male and backcrossing could not be used
and no. 300 died before additional litters
could be produced, the results are inconclusive.
A litter of 6 , two being normal and 4
polydactylous, resulted from the backcross
of no. 1203 with no. 1000. Much variation
was obtained (table 1). No. 1203 was the
only polydactylous female in the first litter from no. 1000 X no. 200, and time did
not permit crosses of no. 1000 with polydactylous females produced in subsequent
litters of this mating.
Although the duplication of digits is obviously under genetic control, it does not
appear that specific variations are controlled by the same factor. In considering
the general trait, rather than specific modifications, it must be concluded that polydactylism is dominant. Although cases of
recessive polydactylism have been described in humans (Cummins, ’34; Oliver,
’40; Snyder, %), the results of the cross
of no. 1000 with no. 1203 rule out such
a possibility in cats. If different types of
polydactylism are taken into consideration
the explanation of a simple dominant gene
is insufficient; variable expressivity indicates the action of modifying genes or
environment. Certainly the fact that the
variations seen in types A and D are
common to all the types raises the possibility that these types are controlled by a
dominant gene, further variation being
controlled by modiPying genes or environment. But why do some (no. 1208 and
1215) have no two feet alike and others
(no. 1209 and 12034) have three variations? Danforth too (’47) noted a lack of
bilateral symmetry. No explanation can
be given, but it is hard to believe that the
uterine environment would be more variable in the region of the hind feet than it
would be in the area of the fore-feet to
thus explain the greater variability of the
hind feet. It is even more difficult to believe there would be enough environmental
variability to produce an animal having a
different type on each foot. To explain the
variation between different feet of the same
cat on the basis of modifying factors, we
would have to assume that each ossification center of each digit was controlled by
a separate modifier. This does not seem
logic a1.
211
SUMMARY
A study of polydactyly in cats was made
to provide precisle anatomical information
and to correlate this with hereditary mechanisms. The 8 antomical types found were
examined by x-rays and dissections, and
dorsal and ventral photographs were taken
for further study. Thirty-one cats were
utilized.
It was found that, although several types
of polydactylism could be described, one
duplication was common to all types. This
involved skeleton, musculature, and innervation of the second digit and was the type
present in the male who fathered all of the
litters. To this basic variation was added
a distal splitting of the lateral second metatarsal or metacaipal in some types, duplication of the 4th digit in others, and an
“integumental” digit, composed only of
skin and a claw. in still others. Homology
was seen in two of the types between foreand hind feet. In some animals one type
was found in the fore-feet and a different
type in the hind feet. In two cases each
of the feet showed a different type. Greater
variation was found in the hind feet than
in the fore-feet.
Crosses were made using a polydactylous
male, two females of differing polydactylous types, and a normal female. The basic
pattern of the male persisted in all polydactylous offspring, but additional variables were added to it. It became obvious
that polydactyly is not caused by a recessive gene in cats. Although simple dominance serves to explain the general trait,
a more complex genetic explanation is
needed to account for the several varieties
of polydactyIy. The possibilities of variation of uterine environment and of activity
of modifying genes are discussed. Genetic
data are insufficient here for conclusions,
but the existence of animals with a different type of dup’iication on each foot makes
doubtful any of the suggested explanations.
LITERATURE CITED
Acker, R. B. 1931 Generalized polydactylism
with concurrent syndactylism. J. Bone Jt.
Surg., 13: 580-582.
Arey, L. B. 1954: Developmental Anatomy, 6th
ed., W. B. Saunders Co., Philadelphia.
Barth, L. G. 1953 Embryolgy. The Dryden
Press, Inc., New York.
212
V. A. CHAPMAN AND FRED N. ZEINER
Cooperman, W. B. 1930 Unusual congenital
conformity of the hand combined with supernumerary toes. J. Bone Jt. Surg., 12: 956-957.
Corrigan, S. H. 1928 An unusual type of a
supernumerary digit. Canad. Med. Assoc. J.,
19: 342.
Cummins, H. 1934 A significant example of
pedunculated post minimus. Anat. Rec., 60:
273-277.
Danforth, C. H. 1947 Morphology of the feet in
polydactyl cats. Am. J. Anat., 80: 143-171.
Horwitz, T. 1940 Supernumerary metatarsal
bone and toe. Am. J. Surg., 50: 578-580.
Howe, F., Jr. 1902 A case of abnormality in
cats’ paws. Am. Nat., 36: 511-526.
Mitchell, R. H. 1928 Supernumerary thumbs.
Brit. Med. J., 1 : 308.
Oliver, C. P. 1940 Recessive polydactylism associated with mental deficiency. J. Hered., 31:
365-367.
O’Rahiily, R. 1946 Supernumerary pollex. Irish
J. M. Sc., p. 636.
Penhallow, D. P. 1928 Unusual case of polydactylia, J. A. M. A., 91: 564-565.
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ANATOMY AND GENETICS OF POLYDACTYLY
V. A. Chapman and Fred N. Zeiner
PLATE 1
Roentgenograms, natural size.
1
Right fore-foot of normal cat, dorsal view.
2
Left fore-foot of types A and C, dorsal view.
3
Right fore-foot of type B, dorsal view.
4
Left hind foot of normal cat, dorsal view.
213
PLATE 2
EXPLANATION OF FIGURES
Roentgenograms, natural size.
214
5
Left hind foot of types D and H, dorsal view.
6
Right hind foot of type E, plantar view.
7
Left hind foot of type F, dorsal view.
8
Right hind foot of type G , dorsal view.
ANATOMY AND GENETICS OF POLYDACTYLY
PLATE 2
V. A. Chapman and Fred N . Zeiner
215
PLATE 3
EXPLANATION O F FIGURES
All figures
9
x
approximately
Yz.
Pads of normal right fore-foot.
10
Pads of left fore-foot of type A. Note peculiarity of palmar pads.
11
Pads of right fore-foot of type B.
12
Paws of left fore-foot of type C. Integumental digit indicated by arrow.
13
Integumental digit of right fore-foot of type C.
14
Pads of normal right hind foot.
15
Pads of right hind foot of type D.
16 Pads of left hind foot of type E.
17
Pads of left hind foot of type F.
18
Pads of left hind foot of type G.
h
19 Pads of left hind foot of type H.
20
216
Integumental digit of right hind foot of type H. The digit is short and on the extreme
left of the figure.
ANATOMY AND GENETICS OF POLYDACTYLY
V. A. Chapman and Fred N. Zeiner
PLATE 3
217
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