TSE BRACHIAL PLEXUS. 765 



^"™,^*° *>? ?°".g extensor of the fore-arm; the other traverses the middle extensor ; 

 and the third is inflected on the tendon of the great dorsal muscle, and passes between 

 the middle and large extensor of the fore-arm. When the radial nerve turns outwards 

 around the arm, and is placed between the anterior brachial and the mass of the 

 oleoranian muscles It furnishes: 1, Muscular branches that pass immediately beneath 

 the extensors of the metacarpus and phalanges ; 2, A sensitive branch that leaves this 

 muscular interstice to become subcutaneous. This cutaneous branch of the radial gains 

 the inner tace ot the fore-arm, and divides in two branches that descend parallel to the 

 median subcutaneous vein. One of these is lost around the carpus ; the other is placed 

 a little in front of the metacarpus, and reaches the metacarpo-phalangeal articulation, 

 ■where it terminates by two principal filaments that constitute the dorsal collaterals of the 

 digits; there is a third which crosses the interdigital to anastomose with the palmar 

 collaterals. 



The ulnar and median nerve of Ruminants lie beside each other, as far as the middle 

 of the arm. This double ccird is situated at the surface of the humeral artery ; at the 

 carpus the two nerves oflfer the same distribution as in the Horse, but beyond this there 

 are some differences. 



The tihiar does not receive a branch from the median at the carpus, and it forms the 

 external plantar nerve or interosseous palmar of the first space, placed at the external 

 border of the flexor tendons. This nerve is reinforced by a filament detached from the 

 external plantar, that joins it a little above the fetlook-joint ; it gives ramuscules to the 

 ergot, and is then continued by the external collateral nerve of the outer digit, into the 

 horny claw. 



The median is continued by the internal plantar, or interosseous palmar of the third 

 space. Towards tlie inferior third of the metacarpus, it divides into three branches : ihe 

 third passes to the external plantar ; the second proceeds to the interdigital space, where 

 it bifurcates to form the internal collateral palmar nerves of the external digit,and external 

 collateral of the internal digit ; the third gives some filaments to the ergot, and passes 

 along the digital region, where it constitutes the internal collateral of the internal digit. 



Pig. — Three fasciculi are detached from the brachial plexus; the posterior is the 

 most voluminous, and furnishes the radial, median, and cubital. 



The branches of the plexus that pass to the trunk and the first rays of the anterior 

 limb much resemble those of Ruminants; the branch oftlie serratus magnus is remarkable 

 for its length and size. 



The median nerve is disposed like that of Solipeds and Ruminants, as far as the carpus ; 

 from this point it passes beneath the flexor tendons of the phalanges, gives filaments to 

 the interosseous palmar muscles, and at the two rudimentary digits divides into four 

 branches : the two upper are the smallest, and form the collaterals of the rudimentary 

 digits ; the inferior two are the longest, and reacli the principal interdigital space, 

 forming the collaterals of the two great digits. 



The ulnar gives off, towards the middle of the arm, a branch that passes to the ulna ; 

 at the ulna it furnishes several muscular branches. The nerve then bends round to the 

 outside of the fore-arm, and on arriving above the pisiform bone, bifurcates : one branch 

 goes along the outer border of the flexor tendons, and is continued by the collateral of the 

 external digit ; the other is placed on the anterior face of the metacarpus, and alto 

 bifurcates to give the external digits their dorsal collateral nerves. 



Cahnivoba. — The four last cervical and first dorsal compose the brachial plexus in the 

 Camivora ; the fifth cervical gives an insignificant filament. When the plexus is un- 

 ravelled, its principal branches are observed to send fibres to each other. 



The number of the distributive branches is the same as in Solipeds, and the dis- 

 position of the superior branches is so analogous as to call for no remark; so we will 

 only describe the anterior brachial, radial, median and cubital nerve. 



The anterior brachial, or musculo-cutaneous, is constituted by a filament froia the sixth 

 cervical and the more voluminous branches coming from the seventh. Placed in front of 

 the axillary artery, this cord arrives at the scapulo-huraeral articulation, where it 

 bifurcates : one of the branches passes forward to the biceps : the other remains alongside 

 the anterior border of the humeral artery, and terminates by a sHghtly recurrent brancli 

 that is buried in the anterior brachial muscle, and by a very fine filament that becomes 

 subcutaneous at the elbow, and descends on the inner border of the_ fore-arm to^ be lost 

 in the vicinity of the carpus. The anterior brachial is, therefore, in these animals, a 

 musculo-cutaneous nerve. The branch uniting it to the median nerve is situated a little 

 below the middle of the humerus, instead of being beneath the axillary aatery, as in 



The radial nerve, in the Dog, is exclusively formed by the eighth cervical ; it receives 

 filaments from the median, ulnar, and axillary nerve, and gives branches to these three. 



