DISEASES. 715 



near the inferior border, or by fibrous bands running from one to 

 the other. The superior border, either convex or straight, is thin 

 and separated from the posterior by an obtuse angle in front of 

 which it presents a deep notch for the passage of the blood ves- 

 sels and nerves. The inferior border is attached, forward, to the 

 basilar and retrosal processes of the os pedis. Behind this it re- 

 flects inward, to continue to the inferior face of the plantar cush- 

 ion. The posterior border, obHque, backward and downward, is 

 slightly convex and unites with the preceding. The anterior 

 border, oblique in the same direction, is more intimately united to 

 the anterior lateral ligament of the articulation and can be sepa- 

 rated from it only by artificial dissection. It sends upon this 

 ligament and upon the anterior extensor of the phalanx, a fibrous 

 extension, which unites with that of the opposite side. 



In their structure, the fibro-cartilages comprehend a mixture 

 of fibrous and cartilaginous tissue, a mixture which is far from 

 being homogeneous and even in the various parts. The more it 

 is examined forward and near the base, the more its substance is 

 seen to resemble that of cartilages proper, being white, flexible, 

 brittle, and homogeneous. Toward its posterior part it loses its 

 character of homogenity, becomes less brittle and presents in its 

 thickness a greater amount of fibrous texture. More posteriorly 

 again, the fibro-cartilaginous structure is more marked. By close 

 attention it seems to show cartilaginous nuclei, isolated, and sur- 

 rounded with an entirely fibrous substance ; and again, at its pos- 

 terior extremity it becomes fibro-greasy with much cellular tissue 

 and unites with the plantar cushion. The vitality of the cartilage 

 is in inverse ratio with its density and consequently is greater in 

 its posterior part than toward the base and its anterior extremity. 

 This fibro-cartilage may easily and more or less completely be- 

 come ossified ; old horses are those which most commonly present 

 this condition, and draught horses are more subject to it than 

 those used to the saddle. It assumes various forms. At times it 

 occupies the entire extent of the cartilage, and at others only at its 

 base ; sometimes the external surface is ossified, while the internal 

 remains in its normal structure ; then again, the ossification exists 

 only anteriorly while the posterior is cartilaginous, and it more 

 rarely happens that the process consists in bony lamellae, which, 

 starting from the base, spread toward various points of its cir- 

 cumference. 



