THE INTEGUMENTARY APPENDAGES. 



801 



Fig. 371. 



Of the veins, at pages 612 to 616 ; 



Of the nerves, at pages 762, 763. 



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

 and the heratogenous membrane. 



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

 v/e gave of this apparatus at page 85, we' said that it was composed of two 

 lateral pieces — the fibro-cartilages, xxnitei behind and below by the ^Zawtor 

 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. FiBRO-OARTiLAGES OP THE Pbdal Bone. — Each of thesc pieces re- 

 presents 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 

 slightly overhangs that of the pedal bone. The internal face is concave, 

 channeled by vascular furrows, and covers, in front, the pedal articulation, 

 and the synovial cul-de-sac which projects between the two lateral ligaments 

 of that joint ; below and behind, it is united to the plantar cushion, either 

 through continuity of tissue, as at the in- 

 ferior border, or by fibrous bands passing 

 from one to the other. The upper border, 

 sometimes 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 tlie digital por- 

 tion. 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 with the anterior lateral liga- 

 ment of the pedal articulation, that it cannot 

 be separated from it except by an artifice 

 of dissection. It sends to this ligament, and 

 to the tendon of the anterior extensor of 

 the phalanges, a fibrous expansion that be- 

 comes fused with that of the opposite side. 



The fibro-cartilages comprise in their 

 structure a mixture of fibrous and cartilagi- 

 nous tissue, though the mixture of these is far from being perfectly homo- 

 geneous, or everywhere in the same proportions. 



The cartilages of the Jore-feet are thicker and more extensive than those 

 of the hind ones. 



(The lateral fibro-cartilages are peculiar to Solipeds.) 



2. Plantar Cushion. — The plantar cushion is a kind of wedge, situated 

 in the space between the two cartilaginous plates of the third phalanx, and 

 between the perforans tendon and the lower part of the horny box. Its shape 



hoeizontal section of the 



horse's foot. 

 Front, or toe of the hoof; 2, Thick- 

 ness of the wall ; 3, Lamince ; 4, 

 Insertion of the extensor pedis ; 5, 

 Os pedis; 6, Navicular bone; 7, 

 Wings of the os pedis; 8, Lateral 

 cartilage; 9,- Flexor pedi^ tendon; 

 10, Plantar cushion; 11, Inflexion 

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

 frog. 



