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. The stipra-scapalar 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 subscapular, 

 and the circumflex, to the pectoral muscles, the axilla, and the shoulder; 

 the internal cutaneous, external ox rnusculo-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 tht^ 

 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 dorscdis carpi idnaris, 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 ^'^ of ^^^ 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 muscido-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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