_ NEUROLOGY. 133 
external respiratory, from the fifth and sixth cervical. It descends obliquely 
outwards behind the brachial plexus, and passing along the serratus magnus, 
supplies it with fasciculi. 4. Zhe supra-scapular form the upper division of 
the plexus. Descending it gives off branches to the supra-spinatus, infra- 
spinatus, teres minor, and to the shoulder-joint. 
The infra-clavicular, or axillary branches, are the thoracic, the sub-scapular, 
and the circumflex, to the pectoral muscles, the axilla, and the shoulder; 
the internal cutaneous, external or musculo-cutaneous, median or brachial, and 
the ulnar, to the anterior and internal aspect of the arm, forearm, hand, and 
fingers; the musculo-spiral, or radial nerve, to the supinators of the forearm, 
hand, and fingers. Some of these branches we shall now notice more in 
detail. 
- The median or brachial nerve is the largest branch of the plexus; it 
generally arises by two roots, one in common with the external cutaneous, 
from the upper part of the plexus, the other internal, from the lower end of 
the plexus in common with the ulnar and internal cutaneous. The brachial 
artery usually separates these two roots, which soon unite into one thick 
cord, passing down superficially as far as the bend of the elbow; at the end 
of the elbow it passes along the brachialis anticus, and perforating the pro- 
nator, descends along the middle of the forearm, and terminates in the hand 
by five or six branches. A little below the elbow this nerve gives off the 
anterior interosseal nerve. . 
. The ulnar nerve arises from the lower part of the plexus in common with 
the internal cutaneous.and the inner head of the median; descending the 
arm, it passes behind the elbow-joint through the groove between the inner 
condyle and the olecranon process; it then passes forwards and descends 
along the ulnar side of the forearm to the carpus, and passing over the an- 
nular ligament close to the pisiform bone, ends in the palm of the hand in 
two branches, a superficial and a deep. A little above the wrist it gives 
off the dorsalis carpi ulnaris, a large branch which winds round the ulna to 
the back of the hand, there dividing into several long branches. 
~Connected to the digital and other sensitive branches both of the median 
and ulnar nerves are.a number of small indurated white bodies, now known 
by the name of Pacinian corpuscles from their discoverer. They appear like 
globules of firm cellular membrane, in size from 3; of an inch upwards, and 
connected to the nerve by a short delicate nervous stem. The corpuscle 
itself is found to consist of a great number of concentric membranous cap- 
sules, with intervening clear fluid. Their function is unknown. Pacini 
suggested that they might in some way be connected with the phenomena 
of animal magnetism ; others see in them an analogy to the electrical organ 
of fishes. They are especially abundant in the mesentery and mesocolon 
of the cat. Similar sessile bodies have recently been discovered by Leidy 
in the intercostal nerves of the boa constrictor. 
The musculo-spiral or radial nerve is the largest branch in the plexus; 
it: proceeds from the middle and lower divisions in common with the cir- 
cumflex nerve, and descending to the elbow there divides into two branches, 
an anterior or radial branch and a posterior or interosseal branch, previously 
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