THE BRACHIAL PLEXUS. 763 



They separate from one another nearly at the insertion of the suspensory 

 ligament into the sesamoid bones. One of them descends in front of the 

 vein ; another passes between the two vessels ; while the third follows the 

 artery behind. They may, therefore, be distinguished, according to their 

 position, into anterior, middle, and posterior (Fig. 349, m, o, b). 



The anterior branch distributes its collateral divisions to the skin on the 

 anterior face of the digit, and its terminal ramusoules in the coronary 

 cushion. 



The middle hranch freq[uently anastomoses with the other two, par- 

 ticularly with the anterior, and to such a degree as to be scarcely dis- 

 tinguished from it; it enters the coronary cushion and the podophyllous 

 tissue. 



The posterior hranch, much more considerable than the preceding, and a 

 veritable continuation of the plantar nerve, is at first superposed on the 

 digital artery, then it is placed immediately behind that vessel. It descends 

 with it to near the basilar process of the third phalanx, follows the pre- 

 plantar uugueal artery into the lateral fissure of that phalanx, and, like that 

 vessel, expends itself in the midst of the podophyllous tissue, as well as in the 

 osseous structure. This branch gives off numerous ramuscules on its course. 

 Of these there may be more particularly noticed : 1, Some posterior 

 divisions, distributed behind the flexor tendons, especially at the fetlock; 

 2, A satellite branch to the artery of the plantar cushion ; 3, A filament 

 arising below the lateral cartilage, passing forward, in proximity to the 

 anterior branch of the arterial coronary circle, and becoming lost in the 

 meshes of the deep venous network of the cartilage ; 4, A small podo- 

 phyllous division, whose point of origin is placed at the same height as the 

 preceding filament, but opposite it, and which descends on the retrossal 

 process, where it traverses the cartilaginous tissue to pass to the podo- 

 phyllous reticulation, after distributing posterior ramuscules to the plantar 

 cushion ; 5, Several extremely fine filaments enlaced around the plantar 

 ungueal artery, and with it penetrating to the interior of the os pedis ; some 

 of these filaments ascend to the nerve of the opposite side."^ 



DIFFERENTIAL CHARAOTEES IN THE BBAOHIAL PLEXUS OF OTHER THAN SOLTPED ANIMALS. 



In the domesticated mammala, the nerves of the brachial plexus do not oifer any very 

 important diiferences in the upper part of the limb ; these only become apparent in its 

 last section. 



EuMiNANTS. — The branches of the plexus, the same in number as in the Horse, are 

 relatively more voluminous than in that animal. In the Ox they are often flexuous in 

 their upper part. In the Sheep, we have found that the diaphragmatic nerve is formed 

 by 'a single filament, detached from the branch the sixth cervical nerve gives to the 

 brachial plexus. There are no differences to signalise in the branch of the angularh and 

 rhomboideus, in the branches of the pectoral muscles, the mbcutaneous thoracic branch, 

 or the anterior brachial or musculo-eutaneous nerve. 



1 It is because we conform to established usages, and are unwilling to force analogies, 

 that we preserve the designations of " plantar nerves," and " digital branches," as well 

 as the above manner of describing them. Comparative anatomy desires other names and 

 a different description ; for it demonstrates that the external plantar nerve corresponds 

 to the interosseous of the first space in pentadaotylous animals ; the internal plantar to 

 the interosseous of the third space, and the branch extending from the internal to the 

 external plantar, to the interosseous of the second space, and whicli only virtually exists 

 in the Horse in 'conseiiuence of the fusion of the second and third metacarpal bone, and 

 which is prolonged to the phalanges. It also shows that the digital branches are the 

 exact representatives of the collaterals of the digits which result, in the pentadaotylous 

 species, from a bifurcation of each interosseous nerve. 



