868 TEE NERVES. 



which, at some points, they cover with their divisions. They separate from one 

 another nearly at the insertion of the suspensory Ugament into tlie 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. 467, M, 0, e). 



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

 anterior face of the digit, and its terminal ramuscules in the coronary cushion. 



The iniddle brancJi frequently anastomoses with the other two, particularly 

 with the anterior, and to such a degree as to be scarcely distinguished from it ; 

 it enters the coronary cushion and the podophyllous tissue. 



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

 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 preplantar ungual 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 par- 

 ticularly noticed : 1 . Some posterior divisions, distributed behind the flexor 

 tendons, especially at the fetlock. 2. A satellite branch to the arteiy of the 

 plantar cushion. 3. A filament arising below the lateral cartilage, passing for- 

 ward, 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 podophyllous division, the origin of which is placed at the same height as 

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

 process, where it traverees the cartilaginous tissue to pass to the podophyllous 

 reticulation, after distributing posterior ramuscules to the plantar cushion. 5. 

 Several extremely fine filaments enlaced around the plantar ungual artery, and 

 with it passing to the interior of the os pedis ; some of these filaments ascend to 

 the nerve of the opposite side.^ 



Differential Characters in the Brachial PLEXCfs of the other Animals. 



In the domesticated Mammals, the nerves of the brachial plexus do not offer any very 

 important differences in the upper part of the limb ; these only become apparent in the nerves 

 of the last section. 



Euminants. — The branches of the plexus — the same in number as in the Horse — are rela- 

 tively more voluminous than in that animal. In the Ox they are often flexuous in tlieir upper 

 part. In the Sheep, the diaphragmatic nerve is formed by a single filament, detached from 

 the branch the sixth cervical nerve gives to the brachial plexus, and which passes over the surface 

 of the scalenus; and a second branch which comes from the fifth pair, runs beneath the 

 ecaleuus, and joins the first on the inner surface of the first rib (Toussaint). Tliere are no 



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

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

 manner of describing them. Comparative anatomy dtsires other names and a different descrip- 

 tion; for it demonstrates that the external plantar nerve corresponds to the interosseous palmar 

 of the second space in pentadactylous animals; and the internal plantar to the interosseous palmar 

 of the third space. It also shows thiit the digital branches are the exact representatives of the 

 collaterals of the digits which result, iu the pentadactylous species, from a bifurcation of each 

 interosseous nerve. 



According to this description, it will be seen that the terminal branches of the median 

 nerve are not only distributed over the posterior face of the digit, but that a good number of 

 filaments are sent to the dorsal face — a remark which has been made in recent years, with 

 reference to the distribution of the collateral palmar neives of the human fingers. 



