Class 6. Mammalia. 



477 



and posterior portions, and attached by its anterior end to the 

 sternum; a clavicle also occurs, extending from the edge of the 

 scapula to the episternum, just as in Eeptiles. In all other 

 Mammalia, however, there is a considerable modification; the 

 coracoid* has become rudimentary, and does not reach the 

 sternum : it fuses early in life with the scapula, and is represented 

 only by a projection from the ventral end of this, the coracoid 

 process. The scapula is usually a broad plate, the upper parD 

 of which generally remains cartilaginous ; it is provided on its outer 



Fig. 387. 



Fig. 388. 



Fig. 387. Eight half o£ ihe shovildei- girdle of a young Platypus, cl 

 clavicle, co' anterior, co posterior portion of the coraooid, I glenoid cavity, sc scapula. — 

 Orig. 



Fig. 388. Bright half of the shoulder girdle of a young Ape; shoulder blade 

 much foreshortened, k spine of the scapula. Other letters as in the preceding figure. — 

 Orig. 



surface with an erect longitudinal '''spine " with a ventral pro- 

 jection, the acromion, to which the outer end of the clavicle 

 is attached; whilst its inner end is connected with the manubrium. 

 In many Mammals, the clavicle is wanting [e.g., in all the Ungulata), 

 or is rudimentiry (Dog), and in these cases the shoulder girdle 

 has no direct connection with the axial skeleton ; in others, e.;/., 

 in digging, climbing, and flying forms, the clavicle is a strong i-oJ- 

 like bone. 



The skeleton of the fore limb consists of the usual parts. The 

 bones of the forearm are usually either about equal in size, or the 

 radius is stronger, at least, at its lower end, whilst the lower portion 

 of the ulna is often rudimentary, though its upper end, which bears 

 the projecting olecranon, is usually well developed. The two bones 

 often cross, since the radius is articulated above to the outer, the 

 ulna to the inner side of the humerus, whilst below, the radius is 

 connected with the inner, the ulna with the outer portion of the 

 carpus : in other cases, however, the distal end of the ulna is pressed 

 right behind the radius, so that no true crossing occurs. The two 



* In young animals, the coracoid is lepresented by two separate ossifications, which 

 fuse later with the scapiila (cf.. Fig. 388.) 



