TIBIA. 91 



and most pronounced, and on the side of the bone, between the 

 external prominence and the external condyle, is a depression, in 

 which the tendons of origin of the extensor pedis and flexor 

 metatarsi muscles are attached. 



PATELLA. 

 (PL. L X.) 



This, the knee-pan or stifle bone, is placed in front of the 

 trochlea of the femur. It is very compact, its anterior surface 

 being irregularly convex and very much roughened for liga- 

 mentous attachment, and its posterior surface smooth to articu- 

 late with the trochlea of the femur, presenting two concavities 

 divided by a ridge, the innermost being the lai'ger, and in the 

 fresh state enlarged still more by a projecting fibro-cartilaginous 

 lip, or process. The superior surface of this bone is broad, 

 uneven, and roughened, giving insertion to the group of muscles 

 called the triceps (or quadriceps) cruralis ; the inferior surface is 

 rough and pointed, and gives attachment to the middle straight 

 ligament of the patella, while the lateral borders and angles have 

 the exter-nal and internal straight ligaments attached. 



The patella is the lever bone of the stifle joint, or it may be 

 regarded as a sesamoid bone, developed in the tendons of the 

 attached muscles, so as to increase their power, enabling them to 

 act at an advantageous angle. It is liable to fracture by muscular 

 contraction, and to luxation ; in the latter case the internal 

 lateral ligament is injured, or may be ruptured. 



TIBIA. 

 (PL. L Y.) 



The tibia, or leg bone, is a long bone, larger at its proximal 

 than its distal end, situated between the femur and the astra- 

 galus, slanting downwards and backwards. 



The shaft is three-sided, possessing outer, inner, and posterior 

 surfaces, all of which are wider above than below. The outer 

 surface, concave superiorly and convex inferiorly, is smooth, and 

 lodges the extensor pedis muscle ; the inner surface, slightly 

 convex from side to side, is smooth, excepting at its superior part, 

 where it gives attachment to one tendon of the biceps rotator 

 tibialis, the sartorius and gracilis muscles, and is covered chiefly 

 by skin, fascia, and a strong periosteum. The posterior surface, 



