232 THE VERTEBRATE SKELETON. 



situated internal or ventral to the ribs. It consists of three 

 bones, a dorsal bone, the scapula, an anterior ventral bone, 

 the precoracoid, and a posterior ventral bone, the coracoid. 



The scapula is a small somewhat rod-shaped bone form- 

 ing about two-thirds of the glenoid cavity. At its proximal 

 end it is closely united with the precoracoid, the two bones 

 ossifying continuously. It tapers away distally, and is directed 

 dorsalwards towards the carapace. 



The precoracoid forms an angle of about 130 with the 

 scapula, with which it is completely fused at its proximal end. 

 Its distal end is somewhat expanded and flattened, and is 

 terminated by a fibrocartilaginous epiprecoracoid which 

 meets its fellow. It takes no part in the formation of the 

 glenoid cavity. 



The coracoid is a large flattened blade-shaped bone form- 

 ing about one-third of the glenoid cavity. It does not meet 

 its fellow in a ventral symphysis, and is terminated by a carti- 

 laginous epicoracoid. The glenoid articulating surfaces of 

 both scapula and coracoid are lined by a thick pad of car- 

 tilage. 



THE ANTERIOR LIMB. 



This is divisible into three portions, the upper arm, fore- 

 arm and manus. 



The upper arm contains a single bone, the humerus. 



The humerus (fig. 40, A, 1) is a stout, nearly straight, some- 

 what flattened bone widely expanded at both ends. At the 

 proximal end is the large hemispherical head, which articulates 

 with the glenoid cavity. Behind the head the bone is drawn 

 out into another large rounded process. Below the head the 

 shaft bears a small outgrowth which is continuous with a 

 larger one on the flexor surface (see p. 29). The bone is 

 terminated distally by the trochlea, consisting of three 

 partially distinct convex surfaces which articulate with the 

 bones of the fore-arm. 



