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Human brachial plexus united into a single cord description and interpretation.

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HUllAN BRACHILIT, 1'1,EXUS UNITED ISTO A
SINGLE CORD
I) EBCHIPTIOP; A N ) I N T EK PRETA TI O S
FOUR F I G U R E S
Evicleiice lias shown that anomalous coiic'litions in the lieripherti1 iiervou s system frequeiitly result froin some change
in the vascular system whereby tlie latter imposes itself in the
path of the former very much in the sanie way as the experimentalist interferes with the nornial course of clevclopmeiit
(Michelson, Jluller, and Ruge).
TEic case uiicler coiisideratioii reveals an aiiomaly of tlie
asillary artery msociated with an irregularity of the brachial
plexus. Two s i n i l a r cases of a brachial plexus with a single
cord h a r e been reported by Rliiller. ('05) and by Xichelsoii
( '20). They \wre priiicipally interested in tlie peculiarities
of the axillary artery, however, f o r their description of the
hrachial plexus is only sufficient to recogiiize the resemblance
hetween the casvs reported b~ them and the present one. F o r
this i*easoii,detailed comparison of the plexus is iiot available,
arid they cliJ iiot discuss the association of these anom 211'1es.
The present case is reported to consider this latter point.
Figure 1 is a n illustration of tlic dissection showing the
single cord of the brachial plexus and the accoiiipaii$iig
artcria axillaris. Although t lie coiiditioii presented by the
brachial plexus coniprises a very gross aiionialy i n the uiiioii
of all its cords and divisions, careful detailed dissection with
the aid of a dissecting microscope after proper maceralioii
(method proposed by Kerr, '18) failed to clisclose any lib411
412
EDWARD SINGER
normal differences in the origins, courses, or destination of
its individual nerve elements (fig. 3 ) . Hence the abnormality
of the plexus lies only in its extraordinary form. The anomaly
has been found to have had no bearing upon the function of
the arm, as confirmed by the hospital report.
The axillary artery lies iriedially to a single united cord,
instead of being located between the three normal cords of
Fig. 1 United cords of tlie brwc.lual plexus ljiiig lateral t o tile axillary artery.
A bundle encircles the axillary artcry to form a root of the radial nerve. The
asillarg vein is cut, tlie stumps are visible medial t o tlie artery.
tlie brachial plexus in a manner which gives them their usual
designation, medial, lateral, and posterior cords. I n the
niicldle of' the arm the artery divides into two branches of
equal size. Oiic braiich, lying anteriorly to the 11. medianus,
assuiiies the position of the a. radialis in the distal part of the
arm. The other branch corresporids to the a. ulnaris (lying
posteriorly t o the 11. niedianus) and gives origin to all the
brariches that normally arise from the a. interossea.
BRACElIAL P L E X U S U N I T E D INTO S I N G L E CORD
413
The united card revealed a hole in its lower end, transmitting a small blo83d vessel (fig. 2 ) which, according to its position, appears to be the embryonic a. axillaris profunda. We
call attention t o this opening because it lies between the two
heads of the n. inedianus.
Emerging from the interval between the anterior and
middle scalene niuscles, the nerve roots C5, C6, C7, C8, and T I
entered into the formation of this single-corded brachi&l
plexus in the following manner :
The fifth and Eiixth nerves (each about 4 em. in length) unite
to give rise to ( 3 common trunk (2.5 em. long), which then
joined the nerve C7.
The seventh nerve, before joining the common trunk, formed
the middle trunk (43 em. long). At its proximal end it gave
off a few fibers to the eighth nerve. The eighth nerve ( 2 em.
long) joined the T1 (2 cm. long) forming the common trunk
(4i em. long). The inferior trunk then joined the united
cord which gave d
f the terminal branches.
I n explanation of this anomaly, Miiller and Senior1 have
demonstrated that the nerve plate of the embryo becomes
perforated by a number of vessels (fig. 4). Of these perforating vessels two become permanent, namely, the a. transversa
colli and the a. axillaris profunda, the latter becoming the
a. axillaris of the adult. While Muller believes that the
perforating vesscds are all arteries, Senior is inclined to think,
and we are of thl: same opinion, that only a few are arteries,
and the network that Muller shows in his pictures represents
mostly veins. These perforations for the passage of vessels
develop into the loop for the n. medianus and the 11. thoracales
anteriores. Further development of the nerve plate consists
in its splitting into bundles and in an enlargement of the
openings through which the arteries pass. I n the present
case, the a. axilkxis profunda did not develop in the normal
manner, remaining in a rudimentary state. It pierced the
nerve plate origj nally, but its subsequent development was
arrested so that further separation of the plate did not ensue.
Personal eommunicr tion from Doctor Senior.
414
EDWARD SINGER
Thus the foramen remained small as in the embryo. Study
of the network of the plexus after maceration shows that the
nerve bundles were differentiated from a normal anlage, but
kept their embryonic juxtaposition through failure of cleavage
which normally is induced by growth of the profunda artery.
\
n
b
Fig.2 The brachial plexus as i t appeared after cutting i t out of the body.
*, the hole in the united cord.
The indications are that the usual separation of the cords
from each other is due to a normal development of the a.
axillaris profunda of the embryo, which persists in the mature
individual as the a. axillaris.
Fig. .‘I The brncliinl plexns nnd tlic coiiipoiiciits rcvenlrd by trnciiig tlicir fibers.
416
The solid coiistitutioii of tlic cord a s observed in this CNSC’
should he reg;ardecl as a result of iioii-clevelol~iiiciit, or r(ilarded clevelop nieiit, of the foetal a. axillaris lxofuiida. Under
these conditioiis, the exist iiig a. axillaris is a coiiipeiisatory
o~cl.-der~lol)mc?nt
of the a. avillaris superficialis.
Fig. 4
Kracliial nerve plate of
ail
enibiyo ( a f t e r E. Jliillrr).
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