THE LIMBS OF THE EOESE 89 



part of each cartilage with the common extensor tendon near its 

 insertion. 



A \. DIGITALBS volares. — During the dissection of the limb in 

 general some of the branches of the volar digital arteries were examined, 

 but some could not be followed until the contents of the hoof had been 

 dissected. 



1. The dorsal and '2. volar branches of the first phalanx have been 

 dissected. The following remain for examination : — 



3. Aa. toricce phalangis tertice. — These leave the digital arteries 

 about the level of the proximal border of the cartilages of the third 

 phalanx, and are distributed mainly on the surface (in the matrix) of 

 the torus. 



4. Rami dorsales phalangis secundec. — The dorsal rami of the second 

 phalanx run round the digit proximal to the distal interphalangeal 

 joint and under cover of the cartilages of the third phalanx and the 

 common extensor tendon. 



5. Rami volares phalangis secundec. — The volar rami arise opposite 

 the foregoing and, by anastomosis, form a transverse connection 

 between the two digital arteries just proximal to the sesamoid bone. 



6. Aa. coronates phalangis tertice. — The coronal arteries are incon- 

 stant in their origin. They frequently arise from the dorsal rami of 

 the second phalanx. Whatever their origin, the arteries supply the 

 coronary matrix. 



7. Aa. dorsales phalangis tertice. — The dorsal arteries of the third 

 phalanx pass through the notch or foramen at the angle of the bone 

 and are distributed in the laminar matrix. 



8. The terminal branch of each digital artery enters the volar 

 foramen of the third phalanx and, in the semilunar canal in the interior 

 of the bone, anastomoses with its fellow vessel to form the terminal 

 arch (arcus terminalis), from which numerous small arteries arise and 

 pierce the foramina on the dorsal surface and at the distal border of 

 the phalanx. 



The insertion of the deep flexor tendon may now be examined. 

 The tendon widens as it crosses the surface of the sesamoid bone — 

 where it is provided with a synovial (mucous) sheath — and is inserted 

 to the flexor area of the third phalanx. 



The proximal interphalangeal articulation (articulatio phalangis 

 secunda?).- — The opposed surfaces of the first and second phalanges are 

 accurately adapted to each other. This, and the presence of strong 

 collateral ligaments, limits the movement to flexion and extension. 

 The articular area of the second phalanx is extended posteriorly 

 by a fibro-cartilaginous glenoidal lip. 



