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 trabeculz and elastic 
fibers, in the meshes of which are masses of fat. The bulbs are soft and loose in 
Coronary 
Wall corium Extensor tendon 
Collateral ligament 
Fig. 718.—Section or Diair or Horse at Coronary Borper or Hoor. 
1, Extenso* 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; 8, podotrochlear or 
navicular bursa; 9, digital vessels; 10, digital nerve. r 
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 
oecur 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 coritum 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 lamine. The nerves are branches of the digital nerves; some fibers 
end in lamellar corpuscles and end-bulbs. 
1The 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. 
