258 VERTEBRATES. 



triangle, and hollowed there to form a. cavity, into which 

 the head of the humerus fits. The coracoid is not a sepa- 

 rate bone in the adult rabbit, but only a curved process 

 attached to the scapula, and overhanging the head of the 

 humerus. The clavicle is a slender, incomplete bone, 

 developed within a ligament which extends from the 

 sternum to the scapula. 



The bones of the fore limb are humerus, radius, ulna, 

 carpal and metacarpal bones, and phalanges. All these 

 are easily recognizable. The humerus is the single bone 

 of the upper arm. The ulna is the larger of the two 

 bones of the forearm. Its enlarged proximal end bears 

 the olecranon process, which forms the angle at the elbow. 

 Both radius and ulna have a thick cap or transverse plate 

 of bone (epiphysis) more or less completely coossified 

 with the shaft of the bone. The small carpal bones are 

 arranged in two transverse TOAVS, three bones in the 

 proximal row, and four in the distal row, with a single 

 minute, roundish bone between the rows, on the median 

 line. The metacarpals are a transverse series of elongated 

 bones (the inner one short) ; and the phalanges (or finger 

 bones) are two in the inner digit or thumb, and three in 

 each of the other digits. 



V. Pelvic Girdle and Leg Bones. In the pelvic girdle 

 the usual three bones of each side are, as usual, fused with 

 each other, and firmly attached to the sacral vertebra. 

 The two sides of the girdle are united also in a ventral 

 symphysis. Each of the three takes part in the formation 

 of the deep cup-shaped acetabulum, in the sides of which 

 the boundaries between them may readily be seen in 

 young specimens. The ilium forms the anterior part of 

 the girdle on each side. It is broadly flattened in front, 

 narrowed behind, and it forms about half of the acetab- 

 ulum. The ischium is posterior and dorsal, and forms 

 about one third of the acetabulum. Its posterior portion 



