THE INTEENAL SKELETON. 1 99 



The tilia is generally the longest bone of the leg, and is some- 

 what triangular in section at its upper part. At the anterior 

 aspect of its upper end is an irregularly shaped prominence 

 called the cnemial process. The lower, or distal, part of the tibia 

 ends in two condyles or antero-posteriorly directed prominences 

 with a median depression forming a pulley-like articular surface 

 or trochlea, which is directed somewhat forwards as well as 

 downwards. On the front of the lowest part of the tibia, just 

 above the condyles, is a deep depression over which a band of 

 bone (a bony bridge) generally passes. 



In front of the junction of the tibia with the femur there is 

 usually a small bone, the patella, answering to our knee-pan. 

 There may be two such bones, while sometimes there is no 

 patella at all. 



The tibia answers to our shin-bone and more. It does so 

 because the distal end of the bone, which is distinct in the 

 young, answers to a portion of our ankle. 



The main, often the only, element of the skeleton of the next 

 segment of the lower limb is termed the tarso-metatarsus. As 

 already said *, it answers to the skeleton of the middle part of 

 our foot which is called the " metatarsus." It consists of 

 metatarsal bones more or less completely fused into one, and 

 something more, since it also includes what answers to a portion 

 of our ankle-bones. Now in human anatomy the skeleton 

 of the whole of the ankle is called the " tarsus," and thus 

 the skeleton' of the " cms " of birds answers to our leg-bones 

 together with the proximal part of our tarsus ; while the skele- 

 ton of the so-called " tarsus " of birds answers to the distal part 

 of our tarsus together with the bones of the middle part of our 

 foot. It is thus clear that the joint by which the so-called 

 " tarsus " of birds articulates with their " crus " does not 

 answer to our ankle-joint. It answers indeed to no conspi- 

 cuously moveable joint which we possess. It answers to the 

 interval between the proximal and the distal parts of our ankle 

 or tarsus. The joint between the " crus " and " tarsus " of 

 birds is thus only analogous to our ankle-joint and is not 

 homologous therewith, i. e. does not bear corresponding struc- 

 tural relations with surrounding parts. 



The iarso^metatarsal bone is of complex nature over and above 

 the fact that it contains elements of the ankle anchylosed with 



* See ante, p. 197. 



