THE THIRD PHALANX 



103 



On either side is a cle- 



sorius), to which the common extensor tendon is attached, 

 pression for the attachment of the collateral ligament. 



The dorsal or wall surface (Facies dorsalis) slopes downward and forward 

 ihe angle of mclmation on the ground plane is about 45 to 50 degrees in front 



Cartilage 



Articular surface 



Extensor process 



Depression for collateral ligament 

 dorsal surface 



Dorsal Angle Distal border 



groove 



Fig. 81. — Third Phalanx of Horse; Lateral View. 

 a, b, Anterior and posterior extremities of cartilage." 



Laterally the height diminishes, and the slope becomes steeper, especially on the 

 medial side. From side to side the curvature is almost semicircular. The surface 

 is rough and porous, resembling pumice stone somewhat. It is perforated by nu- 

 merous foramina of various sizes; a series of larger ones is situated on or near the 

 distal border. On either side the dorsal groove (Sulcus dorsalis)^ passes forward 

 from the angle and ends at one of the 

 larger foramina. In the fresh state this 

 surface is covered by the corium of the 

 wall of the hoof. The distal border is 

 thin, sharp, and irregularly notched; 

 there is commonly a wider notch in 

 front. 



The volar surface (Facies volaris) 

 is arched, and divided into two unequal 

 parts by a curved rough line, the semi- 

 lunar crest (Crista semilunaris) . The 

 larger area in front of the crest is cres- 

 cent-shaped, concave, and compara- 

 tively smooth; it corresponds to the 

 sole of the hoof, and may be termed 

 the sole surface. The part behind the 

 crest is much smaller, and is semilunar; 

 it is related to the deep flexor tendon, 

 and is hence called the flexor surface 

 (Facies flexoria) . It presents a central 

 prominent rough area, on either side of 

 which is the volar foramen (Foramen 

 volare), to which the volar groove (Sulcus volaris) conducts from the angle.' 

 The foramina lead into the semilunar canal (Canalis semilunaris) within the 

 bone, from which small canals lead to some of the foramina of the dorsal sur- 



FiG. S2.^Section of Third Phal.4Nx op Horse, 

 Section is cut approximately parallel with volar sur- 

 face and opens up the semilunar canal (C.5.). Volar for- 

 amina indicated by arrows. 



^ Formerly termed the pyramidal process. 



* Formerly termed the plantar groove and foramen. 



■ Formerly termed the preplantar groove. 



