122 VERTEBRATE ZOOLOGY 



ately back of the coracoids. The bony half is in front of the car- 

 tilaginous portion, which is a broad, thin, bilobed plate. The 

 episternum lies in front of the clavicles. The bony half is behind 

 the cartilaginous portion, which is a thin, round plate. 



Remove the pectoral girdle with the foreleg from the body. 

 Inasmuch as it is not joined with the vertebral column, it may be 

 removed by freeing it from the muscles in which it is embedded. 

 First locate accurately the delicate cartilaginous portions of the 

 sternum and the episternum ; carefully locate also the delicate 

 suprascapula on each side of the body. Then insert the blade of a 

 small scalpel under the suprascapula on one side and free it from 

 the muscles which lie over it. Pass the scalpel down to the scap- 

 ula and then to the ventral portion of the pectoral girdle. Do the 

 same on the opposite side of the body, and finally remove the en- 

 tire girdle with the breastbone from the body. Disarticulate and 

 remove the two forelegs and very carefully clean away the muscles. 



Exercise 28. Draw an outline sketch of the pectoral girdle and 

 breastbone, representing them in one plane; carefully label all 

 their parts. 



The Foreleg. The skeleton of the foreleg is composed of three 

 divisions,— a proximal, a middle, and a distal division. 



The proximal division, or upper arm, is composed of a single 

 bone, the humerus. The head of it, which is cartilaginous, fits into 

 the glenoid cavity and forms the shoulder joint. Just below it 

 on the ventral side is a prominent ridge called the crista ventralis, 

 in which the pectoral muscles are inserted. At the distal end is a 

 large, round projection, on each side of which is a ridge forming 

 the articular surface for the bone of the next division. 



The middle division, or forearm, is composed of a single bone, 

 the radio-ulna. It is formed by the fusion of the radius and 

 ulna, the two bones which are present in the forearm of most verte- 

 brates. The larger part of this bone is the radius. Its proximal 

 end is concave, the projecting process on it being the olecranon, or 

 elbow. Its distal end has two articular surfaces. 



The distal division is composed of the carpus, or wrist, and the 

 hand. The carpal bones are six in number, arranged in two rows, 



