TEE APPENDAGES OF TEE SKIN. 909 



Of the arteries, at pp. 636, 654 ; 

 Of the veins, at pp. 698 to 703. 

 Of the nerves, at pp. 865, 881. 



It remains to notice the complementary apparatus of the third phalanx, and 

 the Tceratogenous memhrane. 



Preparation. — The dissection of the fibro-cartilages is made at the same time as that of the 

 articulation of the foot. A good idea of the shape of the plantar cushion can be obtained in a 

 longitudinal and median section of the digital region (Fig. 493), and on the piece prepared to 

 show tlie subcorneal tissue. This is obtained by two proce<lures. In the fiist, we wait until 

 decomposition has softened the cells between the hoof and the keratogenous membrane, when 

 the hoof can be easily pulled off. In the second, the foot is kept for several hours in boiling 

 water, then held in a vice by the pastern while the tissues around the coronet are slightly cut 

 through ; a pair of shoeing pincers is now employed at the heels in pulling the hoof up and 

 down until it comes off. The foot is then washed to free it from tlie debris. (The hoof can 

 also be removed by prolonged maceration, or l>y roasting on a fire, when it may be cut and torn 

 off by the farrier's knife and pincers). 



Fig. 491. 



A. Complementary Apparatus of the Pedal Bone. — In the indication 

 we gave of this apparatus at p. 117, it was mentioned that it was composed of 

 two lateral pieces — thejibro-cartilages of the pedal 

 bone, united behind and below by the plantar 

 cushion — a fibrous, elastic mass, on which the 

 navicular bone rests, through the medium of the 

 perforans tendon. We will take this distinction 

 as the basis of our study. 



1 . Pibro-cartilages of the Pedal Bone. 

 — Each of these pieces represents a plate flattened 

 on both sides, having the form of an oblique- 

 angled parallelogram, and prolonged behind the 

 third phalanx. The external face is convex, and 

 pierced with openings for the passage of veins ; 

 it sUghtly overhangs that of the pedal bone. The 

 internal face is concave, channeled by vascular 

 furrows, and covers, in front, the pedal articula- 

 tion, and the synovial cul-de-sac that projects 

 between the two lateral Ugaments of that joint ; 

 below and behind, it is united to the plantar 

 cushion, either through continuity of tissue, as 

 at the inferior border, or by fibrous bands passing 

 from one to the other. The upper harder, some- 

 times convex, sometimes rectilinear, is thin and 

 bevelled like a shell ; it is separated from the 

 posterior margin by an obtuse angle, in front of 



which this border is often broken by a deep notch that gives passage to the vessels 

 and nerves of the digital portion. The inferior border is attached, in front, to 

 the basilar and retrossal processes ; behind the latter, it is reflected inwards to 

 become continuous with the tissue on the lower face of the plantar cushion. 

 The posterior border is oblique from before to behind, and above to below, and 

 joins the preceding two. The anterior border is oblique in the same direction, 

 and is united so intimately to the anterior lateral ligament of the pedal articula- 

 tion, that it cannot be separated from it except by an artifice of dissection. It 

 60 



horizontal section of the 

 horse's foot. 

 1, Front, or toe of the hoof; 2, thick- 

 ness of the wall ; 3, laminae ; 4, 

 insertion of the extensor pedis ; 5, 

 OS pedis; 6, navicular bone ; .7, 

 wings of the os pedis; 8, lateral 

 cartilage: 9, flexor pedis tendon; 

 10, plantar cushion; 11, inflection 

 of the wall, or " bar; " 12, horny 

 frog. 



