PELVIC GIRDLE 261 



from well-developed to absent; when small it is often enclosed in ligament; its 

 connexion with the sternum varies accordingly. 



Carnivora have the scapular spine at about the middle of the bone, except 

 in Otariidae where it is nearer the posterior border; it is always well developed 

 as is the acromion. The coracoid is small, the clavicle reduced or absent ; when 

 best developed (Felidae) it does not reach scapula or sternum; it is absent in 

 Pinnipeds and most bears. 



Cetacea have a very broad and flat scapula in most Odontocetes, less broad 

 in Mystacocetes. The spine is reduced, the acromion has a narrow base and is 

 parallel to the coracoid, both being reduced in Megaptcra. None of the whales 

 have a clavicle. 



Ungulata. — All Ungulates have a long and rather narrows capula, the supra- 

 scapula being imperfectly ossified in most Artiodactyls, swine having a number of 

 foramina for the dorsal rami of the spinal nerves in the hne between the two 

 elements. The acromion is distinct in most Artiodactyla, but is lacking in 

 giraffes. In Perissodactyla the spine inclines backwards and there is no acro- 

 mion, while the coracoid is short and blunt. No modern Ungulates have a 

 clavicle, but a transitory one is reported in the sheep embryo. 



Hyracoidea have a small triangular scapula with a small spine but no 

 acromion. The dorsal part of the scapula persists as a suprascapular cartilage. 

 No clavicle occurs. 



Proboscidia have the scapula with a curved dorsal border and a large spine 

 near the anterior margin, this ending in an acromion with a posterior process. 

 The coracoid is small and rounded and no clavicle occurs. 



SiRENiA have a scapula much like that of seals, narrow and curved behind, 

 and with the spina moderate and near the middle of the bone. The acromion 

 is slender, pointing downwards. No clavicle present. 



Premates. — The scapula of the lower primates is narrow, that of the Anthro- 

 poids is broad, with the spine near the anterior margin. Both acromion and 

 coracoid process are large, the latter often somewhat hooked. The well devel- 

 oped -clavicles are connected with both scapula and sternum. 



Pelvic Girdle 



The Tetrapodan pelvis differs from that of fishes in being con- 

 nected with the vertebral column by the intervention of sacral 

 ribs (p. 25). This connexion is the result of the terrestrial habitat 

 and the need of a firmer support of the body on the legs, since it is no 

 longer buoyed up by the water. There is less uncertainty as to the 

 homology of parts in different groups than in the case of the pectoral 

 girdle, but some questions are not yet solved. In the procartilage 

 stage the two halves of the girdle are separate as in fishes, and only 

 with chondrification are the three elements differentiated. These 

 are an ihum dorsal to the acetabulum, below it an anterior os pubis 

 and a posterior ischium, all of which usually ossify, as sometimes 



