42 THE EUXKS AXJi JOINTS. 



shapes in the two sexes : in the female it remains cylindrical as far 

 as the elbow-joint; in the male, on the posterior surface, where 

 the crista deltoidea ceases, a marked ridge (crista medialis) arises, 

 which gradually winds inwards and terminates at the inner condyle. 

 This sexual difference is found in all the three species described in 

 the Introduction, and it would seem that this ridge increases in height 

 during the pairing season. The muscle which arises from this process 

 is the flexor carpi radialig(Fig. 74 Fc), and it attains, in the males, a 

 very large size at the same period ; indeed, it is at its origin twice 

 as broad as in the female. Duges 1 has incorrectly stated that 

 this crista, is a peculiarity of liana temporaria, and is wanting in 

 Rana esculent a. Pouchet 2 first observed that it was a sexual dis- 

 tinction. 



The anterior articular extremity presents a rounded head, which is 

 somewhat flattened externally. The inferior ventral border is sharp, 

 and developed into the above-mentioned bony crest (crista deltoidea] 

 the free border is arched and curved outwards. Above, on the 

 outer surface of the head, is found an eminence which may be 

 a rudimentary tnlerc. mains. The inner half of the head is 

 articular. 



The posterior articular extremity consists of a rounded head (c], 

 attached to the posterior extremity of the shaft ; internal to this is 

 a small trocMea (ty, placed upon the inner condyle. The external 

 condyle is but small. The head is embraced by these condyles. 

 Upon the under surface, above the head, is the fossa cnlitalu 

 anterior. The structure of the two articular extremities of the hu- 

 merus differs ; the upper, as in long bones generally (see page 16), 

 consists of hyaline cartilage surrounded by calcified cartilage, which 

 again is covered by hyaline articular cartilage ; the lower extremity 

 is composed of spongy bone, with roundish marrow spaces, and for 

 the most part covered by a layer of calcified cartilage. 



The shoulder-joint. The socket is formed by the posterior border 

 of the scapula, by both the processes of that bone, the outer portion 

 of the coracoid, and besides these by cartilage, which forms the 

 articular surface already described (Fig. 33). In the macerated 

 bone the floor of the socket opens dorsally into a fossa 

 between the processes of the scapula (Fig. 32). This opening, in 

 the natural condition, is closed by synovial membrane only; the 

 cartilage covering the rest of the space being absent (the sac may 



1 I.e., p. fiS. 2 Compt. rend. vol. XXV, 1847, p. 761. 



