134 SKELETON OF THE OX 



below. The proximal extremity unites with the shaft at about three and one-half 

 years, the distal at three and one-half to four years. 



The tibia resembles that of the horse rather closely, but is somewhat shorter. 

 The shaft is distinctly curved, so that the inner side is convex. The posterior 

 surface is not divided into two areas, and the linese musculares are fewer and extend 

 up higher than in the horse. The articular grooves and ridge of the distal end are 

 almost sagittal in direction, and present an extensive but shallow synovial fossa. 

 The external groove is separated by a sharp ridge from an outer area which is for 

 articulation with the external malleolus. The anterior part of the internal malle- 

 olus is prolonged downward and has a pointed end. The groove Ijehind it is broad 

 and well defined. Externally there is a deep narrow groove which separates two 

 prominences. The proximal extremity fuses with the shaft at three and one-half 

 to four years, the distal at two to two and one-half years. 



The fibula usually consists of the two extremities only. The head is fused with 

 the external condyle of the tibia and bears a small Ijlunt-pointcd prolongation 

 below. The distal end remains separate and forms the external malleolus (some- 

 times called the os malleolare). It is quadrilateral in outline and compressed from 

 side to side. The proximal surface articulates with the distal end of the tibia, and 

 bears a small spine which fits into the groove on that bone. The distal surface 

 rests on the fibular tarsal, and the inner articulates with the external ridge of the 

 tibial tarsal bone. The outer surface is rough and irregular. 



The early cartilaginous fibula is complete, but later the shaft is reduced and is 

 usually represented by a fibrous cord Avhich connects the two ends. In some cases, 

 however, the upper part undergoes partial ossification, forming a slender rod which 

 is usually united with the outer border of the tibia and is joined to the head by 

 fibrous tissue. 



The patella is long, narrow, and very thick. The anterior surface is strongly 

 convex and very rough and irregular. The articular surface is convex from side 

 to side and nearly straight in the vertical direction. The large prominence on the 

 inner side for the attachment of the accessory cartilage allows prompt determina- 

 tion of the side to which the bone belongs. The apex is more pointed than in the 

 horse. 



The tarsus consists of five pieces; the central and fourth, and the second and 

 third tarsal bones are fused. 



The tibial tarsal bone is relatively long and narrow, and is somewhat flattened 

 from before backward. It bears a trochlea at either end. The groove and ridges 

 of the proximal trochlea are not spiral, but almost sagittal; the outer ridge is the 

 wider, and articulates with both tibia and fibula. The distal trochlea consists 

 of two condyles divided by a groove, and articulates with the combined central 

 and fourth tarsals. The posterior surface bears a large oval facet for articulation 

 with the fil)ular tarsal; this occupies most of the surface, and is convex and grooved 

 from above downward. The outer surface presents two facets for articulation with 

 the fibular tarsal, and is excavated and rough elsewhere. The inner surface bears 

 a tuberosity at its upper part, and is flattened below. 



The fibular tarsal l)one is longer and more slender than in the horse. The 

 distal part of the body is compi'cssed laterally, and bears a i)rojection in front which 

 articulates with the external malleolus. The tuber calcis is marked posteriorly by 

 a wide shallow groov(\ which is coated with cartilage in the fresh state. 



The central and fourth tarsals are fused to form a large bone (Os centrotarsale 

 quartum, scapho-culioid), which extends across the entire width of the tarsus and 

 articulates with all of the other bones. Th(> gn^ater part of the upper surface is 

 molded on the distal trochlea of the tibial tarsal, and its inner part rises high above 

 the rest posteriorly. Externally there is a narrow undulating surface for articula- 

 tion with the distal end of the fibular tarsal bone. The posterior surface bears two 



