OSTEOLOGY AND ARTHROLOGY 85 



say that in these latter the trochlea and the condyles are 

 almost completely separated. 



There is another modification in regard to the promi- 

 nence and extent of the two lips of the trochlea. In 

 man, the external lip of the trochlea reaches higher than the 

 internal, and it is more prominent in front. In the dog, 

 these lips are equal with regard to thickness, but the 

 external still reaches higher than the internal ; in the 

 cat, they are equal in every respect ; in ruminants and 

 solipeds the internal lip is wider, thicker, and rises higher 

 than the external. 



In animals the trochlea is, as a general rule, narrower 

 than in man, and the condyles are more prominent pos- 

 teriorly ; so that, when viewed from one of the lateral 

 aspects, the inferior extremity of the femur is, in them, 

 better developed in the antero-posterior direction. 



In birds, the femur is shorter than the bones of the leg ; 

 its great trochanter is in contact with a prominence which 

 occupies the posterior part of the border of the cotyloid 

 cavity. Instead of articulating at the level of the knee, 

 with the knee-cap and tibia only, as in man, it articulates, 

 in addition, with the superior extremity of the fibula. A 

 similar arrangement is found in marsupials and reptiles. 



The Knee-cap. — This bone, developed in the thickness of 

 the tendon of the triceps muscle of the thigh, is in contact, 

 by its posterior surface, with the femoral trochlea. The 

 two articular surfaces which are applied to the lips of the 

 trochlea present, with regard to their extent, an inequality 

 which is in proportion to the arrangement which we have 

 above indicated — that is, while in man it is the external 

 surface which is the larger, in the horse it is the internal. 

 We shall see what the general form of the knee-cap is 

 when we come, later on, to study more particularly the 

 posterior limbs of some animals. 



The Leg 



The skeleton of the leg consists of two bones : the tibia 

 and the fibula. The tibia is the more internal and the 



