318 VERTEBRATE ZOOLOGY 



The skeleton of the foreleg is made up of three divisions, a 

 proximal, a middle, and a distal division. The proximal division 

 is formed of the humerus, a large cylindrical bone. At its upper 

 end are the head of the humerus, by which it articulates with the 

 scapula, and two prominences, of which the outer, or lateral, one 

 is the greater tuberosity, and the inner one the lesser tuberosity. 

 Along the anterior side of the humerus below the tuberosities is 

 the deltoid ridge, to which muscles are attached. At the lower 

 end of the humerus, and on its anterior side, are the capitulum, 

 with which the radius articulates, and a depression called the radial 

 fossa ; on its posterior side is the deep olecranon fossa, in which 

 the olecranon articulates. 



The middle division of the leg is formed of the radius and the 

 ulna, which articulate with the distal end of the humerus. The 

 ulna is the hindermost of these two bones, and possesses at its 

 proximal end the large olecranon process, which articulates in the 

 olecranon fossa and forms the elbow. The articular surface of 

 the ulna is formed by the semilunar notch, a deep depression just 

 back of the olecranon process. The radius lies in front of the ulna. 



The distal division of the leg is formed by the carpus, or wrist, 

 and the manus, or hand. The carpal bones are nine in number, 

 arranged in two rows, four being present in the proximal and five 

 in the distal row. The hand is composed of the metacarpal bones 

 and the digits. The metacarpals are five in number, of which the 

 first is very short. The digits also number five, each one being 

 composed of a group of bones called the phalanges. The first 

 digit, which corresponds to the thumb, is composed of two pha- 

 langes ; the others have three each. 



Exercise 40. Make a drawing showing all the bones of the leg. Care- 

 fully label all. 



The posterior extremities are made up of the pelvic girdle, or 

 pelvis, and the hind legs. The pelvic girdle is formed by two bones, 

 the right and left innominate bones, which together form an arch. 

 This arch articulates dorsally with a portion of the spinal column 

 called the sacrum ; ventrally the two innominate bones meet and 

 unite in the midventral line, this union being called the symphysis 



