XII 



PHYLUM CHORDATA 



501 



off behind. At the narrow lower end of the scapula is a 

 concave surface, the glenoid cavity, into which the head 

 of the humerus fits, and immediately in front of this is a 

 small inwardly curved process, the coracoid process (c), 

 which is represented by two separate ossifications in the 

 young rabbit. A slender rod, the clavicle (ct), is con- 

 nected with the acromion process externally and with the 

 sternum internally by means of fibrous tissue. 



At the proximal end f 



of the humerus are to 

 be recognised: (i) A 

 rounded head for ar- 

 ticulation with the 

 glenoid cavity of the 

 scapula ; (2) externally 

 a greater; and (3) in- 

 ternally a lesser tuber- 

 osity for the insertion 

 of muscles. At the 

 distal end are two ar- 

 ticular surfaces, one 

 large and pulley-like, 

 trochlea, for the ulna; 

 the other smaller, capi- 

 tellum, for the radius : laterally are two prominences or 

 condyles, an internal and an external. 



The radius and ulna are firmly fixed together so as to be 

 incapable of movement, but not actually ankylosed. The 

 radius articulates proximally with the humerus, distally with 

 the scaphoid and lunar bones of the carpus. The ulna pre- 

 sents on the anterior aspect of its proximal end a deep fossa, 

 the greater sigmoid cavity, for the trochlea of the humerus ; 

 the prominent process on the proximal side of this is the 



FIG 



300. Lepus cuniculus. Shoulder-girdle 

 with anterior end of sternum of young speci- 

 men, a, acromion; /, pre-scapular fossa; 

 c, coracoid; cl, ossified clavicle; ma, meta- 

 cromion; mss, meso-scapular segment; ost, 

 pre-sternum; pc, pre-coracoid ; pf, post-scapu- 

 lar fossa; sr~, sternal ribs. (After Flower.) 



