98 



THE SKELETON OF THE HORSE 



face is small, being encroached upon by the proximal articular surface. 

 surface bears a tubercle on its distal part.-^ 



The volar 



The Carpus as a Whole 

 The bones of the carpus, exclusive of the accessory, form an irregular quadran- 

 gular mass, the width of which is about twice the height or the dorso-volar diameter. 

 The dorsal sxirface is convex from side to side, depressed along the line of junction 

 of the two rows, and prominent below. The volar surface is in general sHghtly 

 convex, but very irregular. It forms with the accessory 

 carpal the carpal groove (Sulcus carpi), which^n the recent 

 state is rendered smooth by the volar ligament; it is con- 

 verted into the carpal canal (Canalis carpi) for the flexor 

 tendons by the transverse carpal ligament, which stretches 

 across from the accessory bone to the medial side. The 

 proximal surface is widest medially and is elevated in front, 

 concave behind ; it is entirely articular and adapted to the 

 carpal articular surface of the radius. The distal surface 

 is also articular and is irregularly faceted in adaptation to 

 the surfaces of the metacarpal bones; each of the distal 

 bones usually articulates with two metacarpal bones, but 

 sometimes the third rests on the third metacarpal only. 

 The medial and lateral surfaces are both irregular and 

 rough, the former being the wider. With the exception of 

 the accessory, ulnar, and second, each bone articulates 

 with two bones of the other row. 



Development. — Each ossifies from a single center. 



McIV 



McIII 



McII 



Fig. 76. — Left ^Ietacarpal 

 Bones of Horse; Volar 

 View. 



1 , Nutrient foramen of 

 large (third) metacarpal bone; 

 2, 3, 4, proximal extremities; 5, 

 surface for attachment of sus- 

 pensory'' ligament ; 6, sagittal 

 ridge of distal end of large meta- 

 carpal bone; 7, 7', distal ends of 

 small (second and fourth) meta- 

 carpal bones. 



77. — Phoximal Extremities of Left Metacarpal Bones of Horse; Eni> 



View. 

 , Facets for second carpal bone; 3, 3', facets for third carpal bone; 4, 4', facets 

 for fourth carpal bone; 5, metacarpal tuberosity. 



THE METACARPUS 



Three metacarpal bones (Ossa metacarpalia) are 

 present in the horse. Of these, only one, the third or 

 large metacarpal bone, is fully developed and carries a 

 digit; the other two, the second and fourth, are much 

 reduced, and are commonly called the small metacarpal or '^ splint" bones. 



The Third or Large Metacarpal Bone 



This (Os metacarpale tertium) is a very strong long bone, which is situated ver- 

 tically between the carpus and the first phalanx. It consists of a shaft and two ex- 

 tremities. 



^ This bone is probably equivalent to the fourth and fifth carpals of forms in which five 

 carpal elements are present in the distal row. 



