MAMMALS. 



359 



from the auditory meatus to the base of the nose, the other 

 from the base of the nose to the most prominent part of the 

 frontal bone. Less used is the system in which the lines inter- 

 sect at the insertion of the teeth in the upper jaw. In man 

 Camper's angle varies from 70° to nearly 90°. In monkeys 

 from 60° (^Chrysothrix') to 35" or 30° ; in other mammals it is 25° 

 or lower. 



The hyoid arch is connected dorsally with the otic capsule, 

 ventrally with the first branchial (Fig. 31). In it ossifications 

 take place which proceed to varying extents. The whole arch 

 may ossify, giving the separate elements, basi-, hypo-, cerato-, 

 epi-, and stylohyal, or the median portion on either side may be 

 converted into a stylohyal ligament, the stylohyal element fus- 

 ing with the skull and forming the styloid process, while the 

 basi- and epihyals fuse to form the body and lesser horn of a 

 single hyoid bone. The first branchial arch also fuses with 

 this, contributing to the body, and forming a greater horn on 

 either side. There is also a ligamentary connection with the 

 second and third branchial arches (thyroid cartilage, p. 28). 



The pectoral girdle shows many variations from the typical 

 condition, for while the scapula is always present, the coracoid, 



A B 



Fig. 347. Pelvis (yi) of young Ornithorhynchus ; {B) oi calf, after Boas, 

 yi, acetabulum; /Z, ilium; 73', ischium; j?/, marsupial bone; /", pubis. 



except in the monotremes, is reduced to a small element — the 

 coracoid process — fused to the scapula. The presence or ab- 

 sence of a clavicle is correlated with habits ; flying, digging, and 

 climbing mammals having it, while it is absent in whales, ungu- 

 lates, and many others. In rodents and carnivores it is reduced, 

 and has only ligamentary connections. The pelvis, on the other 



