130 SKELETON OF THE OX 



lates with the uhiar carpal only. The first carpal is absent. The second and third 

 carpals are fused to form a large quadrilateral bone. The fourth carpal is a smaller 

 quadrilateral bone. 



The metacarpus consists of a large metacarpal and an external small meta- 

 carpal bone. The large metacarpal bone (Mc. 3 + 4) results from the fusion of the 

 third and fourth bones of the foetus, and bears evidences of its double origin even 

 in the adult state. The shaft is shorter than in the horse, and is relatively wider and 

 flatter. The anterior surface is rounded, and is marked by a vertical vascular 

 groove connecting two canals which traverse the ends of the shaft from before 

 backward. The posterior surface is flat and presents a similar but much fainter 

 groove. The borders are rough in the upper third. The proximal end bears two 

 slightly concave facets for articulation with the bones of the lower row of the car- 

 pus; the inner area is the larger, and they are separated by a ridge in front and a 

 notch behind. The outer angle has a facet behind for the small metacarpal bone. 

 The inner part of the extremity has anterior and posterior tuberosities. The distal 

 end is divided into two parts by a sagittal notch. Each division bears an articular 

 surface similar to that in the horse, but much smaller. The medullary canal is 

 divided into two parts l)y a vertical septum which is usually incomplete in the adult. 



The small metacarpal l)one (Mc. 5) is a rounded rod about an inch and a 

 half (ca. 3.5 to 4 cm.) in length, which lies against the upper part of the outer border 

 of the large bone. Its upper end articulates wdth the latter, but not with the carpus. 

 The lower end is pointed. 



Four cartilaginous metacarpals are present in the early foetal state, viz., the second, third, 

 fourth, and fifth. The second commonly either disappears or unites with the third; sometimes 

 it develops as a small rod of Ijone. The third and fourth graduallj^ unite, but can be cut apart 

 at l)irth. Each has three centers of ossification; the proximal epiphysis fuses with the shaft 

 before l^irth, the distal at two to two and one-half years 



Four digits are present in the ox. Of these, two — the third and fourth — are 

 fully developed and have three phalanges and three sesamoids each. The second 

 and fifth are vestiges and are placed behind the fetlock; each contains one or two 

 small bones which do not articulate with the rest of the skeleton. 



The first phalanges are shorter and narrower than in the horse and are three- 

 sided. The interdigital surface is flattened and its posterior part bears a promi- 

 nence for the attachment of the interdigital ligaments. The proximal extremity is 

 relatively large, and is somewhat compressed from side to side. The articular 

 surface is concave from before backward and is divided by a sagittal groove into 

 two areas, of which the abaxial one is the larger and higher. Behind these are 

 two facets for articulation wath the sesamoid bones. The posterior surface bears 

 two tuberosities separated by a deep depression. The distal extremity is smaller 

 than the proximal, especially in the antero-posterior direction. Its articular 

 surface is divided by a sagittal groove into two convex facets, of which the abaxial 

 one is decidedly the larger. There are depressions on either side for ligamentous 

 attachment. The bone consists at birth of two pieces — the distal end and the fused 

 shaft and upper extremity. Union occurs at one and one-half to two years. 



The second phalanges are about two-thirds of the length of the first and are 

 distinctly three-sided. The proximal articular surface is divided by a sagittal 

 ridge into two glenoid cavities, of which the al)axial one is much the larger. There 

 is a central prominence in front and two lateral tubercles behind. The distal ex- 

 tremity is smaller than the proximal. Its articular surface encroaches consider- 

 ably on the anterior and posterior sin-faces, and is divided into two lateral parts by 

 a groove. There is a deep depression for ligamentous attachment on the inter- 

 digital side. The bone contains a small medullary canal. The distal end unites 

 with the rest of the bone about the middle of the second year. 



The third phalanges resemble in a general way one-half of the bone of the horse. 



