THE SKELETON ra! 
Phylogenetically, the oldest elements of the pectoral girdle 
are the scapula and coracoid, and of the pelvic girdle the 
ischium and pubis; for though in certain Fishes the clavicle and 
the ilium are indicated, they are only fully developed from 
the Amphibia upwards. 
Fig. 51 is the ventral view of the pectoral girdle of a 
tailed Amphibian. It shows that the clavicles (cl.) are directed 
forwards (i.e. towards the head), and that the coracoids (co.) 
overlap each other ventrally. The edges of the latter, which 
are connected by fibrous tissue, only loosely overlie the small 
so-called “ sternum ” (s#.). The connection between the coracoids 
Fic. 51.—PECTORAL GIRDLE OF A TAILED AMPHIBIAN, FROM THE 
VENTRAL SIDE. 
cl., clavicle ; co., coracoid ; ar., shoulder-joint ; st¢., so-called “sternum.” 
and the sternum becomes much closer in Reptiles and Birds, and 
persists in the lowest Mammals. The withdrawal from this 
connection seen in the higher Mammalia is proportionate to the 
greater development of the antero-ventral element of the pectoral 
girdle, the clavicle. Through the mediation of this bone the 
scapula finds a new support upon the sternum, and thus the limb, 
being the farther removed from the trunk, attains far greater 
freedom of movement. 
The expanded coracoid of the lower Vertebrata is, in Man, 
represented by an apparent process of the upper edge of the 
scapula, called the processus coracoideus (co., Fig. 52). This serves 
as a point of origin and attachment for certain ligaments and 
