154 SKELETON OF THE OX 
The shaft is distinctly curved, so that the medial side is convex. The posterior 
surface is not divided into two areas, and the lines 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 lateral groove is separated by a sharp ridge from an outer area which is for 
articulation with the lateral malleolus. The anterior part of the medial malle- 
olus is prolonged downward and has a pointed end. The groove behind it is broad 
and well defined. Laterally 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. 
Tuber calcis 
Tuber 
calcis 
M.m. r 
M.1. 5 
Le 
BOT 
Mt. 2 
Mt.3+4 
Mt. $+4 
Fic. 158.—Ricur Tarsts anp Apsacent Bones or OX; Fic. 159.—Ricut Tarsus anp ADJACENT BON=&S OF 
Menta View. Ox; Dorso-LATERAL VIEW. 
M.m., Medial malleolus; M. /., lateral malleolus (distal end of fibula); 7, tibia; 7’. ¢., tibial tarsal bone; 7. /., fibular 
tarsal bone (sustentaculum); J. c.+4, fused central and fourth tarsal bones; 7’. 1, first tarsal bone; T.2+8, fused 
second and third tarsal bones; Mt. 2, small or second metatarsal bone; Mt. 3+ 4, large metatarsal or fused third and 
fourth metatarsal bones; 1, groove for tendon of flexor digitalis longus; 2, groove for deep flexor tendon. 
The fibula usually consists of the two extremities only. The head is fused with 
the lateral condyle of the tibia and is continued by a small, blunt-pointed prolonga- 
tion below. The distal end remains separate and forms the lateral 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 medial articulates with the lateral ridge of the 
tibial tarsal bone. The lateral surface is rough and irregular. 
The early cartilaginous fibula is complete, but later the shaft is reduced to the 
small prolongation noted in speaking of the head and a fibrous cord which connects 
it with the distal end (lateral malleolus). In some cases, however, the upper part 
undergoes partial ossification, forming a slender rod which is usually united with 
the lateral border of the tibia and is joined to the head by fibrous tissue. 
