14 



Profs. D. Ferrier and G. F. Yeo. 



[Mar. 24, 



digital nerves were derived from the first dorsal and eighth cervical 

 nerves respectively. 



Passing from these experimental researches in the lower animals to 

 observations in man, we have a fact of considerable significance in 

 reference to the functional relations of the roots of the brachial 

 plexus, which was first pointed out by Erb (" Diseases of the Peri- 

 pheral Cerebro- Spinal Nerves," in Ziemssen's " Cyclopaedia of the 

 Practice of Medicine," vol. xi, p. 561). By faradisation over the 

 brachial plexus, at a point corresponding with the exit of the sixth 

 cervical nerve from between the scaleni muscles, the deltoid, biceps, 

 brachialis, and supinator longus can be thrown into simultaneous con- 

 traction. At the same time, he says it is difficult to avoid the 

 musculo-spiral nerve, which can also, however, be separately excited. 

 We have ourselves found extension of the wrist a constant accompani- 

 ment of the action of the above muscular group when it is at all distinct. 

 Prom the collocation of the muscles affected in atrophic spinal 

 paralysis, it has been ably argued by E. Reraak (" Zur Pathogenese 

 der Bleiliihmungen, Archiv fur Psychiatrie," 1876; and " Ueber die 

 Localisation Atrophischer Spinallahmungen und Spinaler Muskel- 

 atrophien/' ibid., 1879) that functionally related or synergic muscles 

 are represented together in the anterior horns of the spinal cord ; and 

 he indicates, more or less tentatively, the probable position of the 

 centres of certain brachial and crural muscular groups in the cervical 

 and lumbar portions of the cord respectively. 



With the view of throwing lig-ht on these various questions by 

 physiological researches, which may be regarded as almost directly 

 applicable to man, we have made a series of experiments on the 

 motor roots of the brachial and lumbo-sacral plexuses in monkeys. 



The brachial plexus in the monkey corresponds- in its constitution, 

 configuration, and distribution almost exactly with that of man. It 

 is formed by roots from the fourth, fifth, sixth, seventh, and eighth 

 cervical, and the first dorsal nerves. These unite and form the larger 

 nerve-trunks in essentially the same way as in man. The phrenic 

 nerve, however, arises from the third and fourth cervical, and does 

 not, so far as we have examined, receive a branch from the fifth, as is 

 usually the case in man. 



The lumbar and sacral plexuses, however, do not at first sight 

 appear to correspond, at least as regards the origin of the roots which 

 enter into their composition. This is owing to the fact that there are 

 seven lumbar vertebrae in the monkeys we have examined. If, how- 

 ever, we detach the first lumbar vertebra and add it to the dorsal, so 

 as to make thirteen dorsal vertebrae, and count the last lumbar as the 

 first sacral, the harmony, as regards the mode of distribution of the 

 several roots, becomes complete. And, in one case which we examined, 

 there were rudimentary ribs attached to the first lumbar vertebra. It 



