894 



THE SENSE ORGANS AND SKIN OF THE HORSE 



The digital cushion (Torus digitalis) is a wedge-shaped mass whicn overlies the 

 frog. It presents for description four surfaces, a base, and an apex.' Its deep 

 surface faces upward and forward and is connected with the distal fibrous sheath of 

 the deep flexor tendon. The superficial surface, covered by the corium of the frog, 

 is moulded on the upper face of the frog. The sides are related chiefly to the 

 cartilages of the third phalanx; distally the cushion is closely attached to the 

 cartilages, but higher up a rich venous plexus intervenes. The base, situated 

 posteriorly, is partly subcutaneous, and is divided by a central depression into two 

 rounded prominences termed the bulbs of the cushion. The apex lies below and 

 is adherent to the terminal part of the deep flexor tendon. The cushion is poorly 

 supplied with vessels. It consists of a feltwork of fibrous trabeculae and elastic 

 fibers, in the meshes of which are masses of fat. The bulbs are soft and loose in 



Coronary 

 Wall corium 



Extensor tendon 



Collaleral ligament 



Fig. 718. — Section of Digit of Horse at Cohonary Border of Hoof. 

 1, Extensor process of third phalanx; 2, distal end of second phalanx; 3, distal sesamoid or navicular bone; 4, 

 deep flexor tendon; 5, digital cushion; 6, cartilage of third phalanx; 7, 7, cavity of coffin joint; podotrochlear or 

 navicular bursa; 9, digital vessels; 10, digital nerve. 



texture and contain a relatively large amount of fat, but toward the apex the cushion 

 becomes denser and more purely white fibrous in structure. Branched coil glands 

 occur chiefly in the part of the cushion which overlies the central ridge of the frog. 

 Their ducts pursue a slightly flexuous course through the corium and pass in a spiral 

 manner through the frog. Their secretion contains fat. 



Vessels and Nerves. — The corium is richly supplied with blood by the digital 

 arteries. The veins are valveless, and form remarkable plexuses which communi- 

 cate freely with each other and are drained by the digital veins. The lymph vessels 

 form subpapillary plexuses in the corium of the sole and frog, and a wider-meshed 

 plexus at the base of the digital cushion. A lymph vessel lies in the attached edge 

 of each of the laminae. The nerves are branches of the digital nerves; some fibers 

 end in lamellar corpuscles and end-bulbs. 



1 The cushion is to be regarded as a special modification of the subcutaneous tissue, bearing 

 on its superficial face the corium of the frog. It is an important factor in diminishing concussion. 



