THE LIMBS OF THE HORSE 87 



Dissection. — The digital torus should be removed entirely, and the 

 two surfaces of the ungual cartilages exposed and cleaned. In conduct- 

 ing this operation the dissector must preserve the arteries and nerves of 

 the region, and, at the same time, observe the venous plexuses from 

 which the digital veins take their origin. 



The caktilages of the third phalanx (cartilagines phalangis 

 tertia). — Tiiese, the ungual cartilages as they are sometimes called, are 

 attached to the angles of the third phalanx, and thus, in a manner, 

 increase the area to which the matrix and other soft parts of the digit 

 are adherent. In the young animal the greater part of the cartilage 

 composing them is of the hyaline variety ; but as age advances a fibrous 



Wall of hoof. 



Laminar matrix. 



Digital torus 



Inflected part 

 of wall ("bar""). 



, Third phalanx. 



Terminal arch of 

 a. digitalis. 



Cuneus {" frog"). 

 Ftg. 61. — Transverse Section of the Foot at the Level Indicated by Line B in Fig. 59. 



development ensues, beginning at the periphery and gradually spreading 

 inwards, until almost the whole structure is converted into fibro- 

 cartilage. Pathologically a considerable extent of the cartilage may be 

 converted into bone ; and some amount of bone formation in that part 

 of the cartilage next to the third phalanx may be regarded as the 

 natural accompaniment of age. 



The superficial surface of each cartilage is convex and smooth and 

 covered with a venous plexus from which vessels pierce the cartilage 

 to gain its deeper face. It is important to note that, while the lower 

 part of this surface gives attachment to matrix and is therefore 

 enclosed within the hoof, the upper part is beyond the border of the 

 hoof and can consequently be felt through the skin. 



The deep surface of each cartilage is concave and intimately 

 adherent to the digital torus posteriorly, while anteriorly it covers 



