148 



ZOOLOGY. 



bingle protuberance at its anterior end and a double one 

 behind ; it has no posterior zygapophyses ; its tranverse 

 processes are stout and backwardly directed and give 

 articulation to the pelvic girdle hence it is the sacral 

 vertebra (cf. chap, vii., 7). The urostyle shows signs of 

 imperfect segmentation at its anterior end, there being a 

 pair of foramina for the exit of a last pair of spinal nerves , 

 posteriorly it tapers almost to a point. 



There are no ribs to any of the vertebra. The vertebra; 

 are all cartilage-bones, but they have no epiphyses. 



11. Limb-Girdles and Limbs. The pectoral girdle (fig. 



73) differs but 

 little from the 

 typical con- 

 dition (fig*. 

 35 and 36, 

 p. 71). The 

 dorso - lateral 

 segment is 

 partly ossified 

 as the scapula; 

 the remainder 

 is cartilage, 

 though largely 



calcified, and is termed supra-scapula/ The antero- ventral 

 portion is cartilaginous (pre-coracoia) but covered over by 

 the clavicle the only membrane-bone other than those of 

 the skull. The postero-ventral portion is a stout cartilage- 

 bone, the coracoid. Between the prccoracoid and coracoid 

 comes a fenestra like the obturator fenestra of the rabbit's 

 pelvic girdle, and similarly perforated by a passage for a 

 nerve of the brachial plexus. In the median ventral line 

 cartilage persists as a symphysis, but it is extended anteriorly 

 and posteriorly into what is commonly called the sternum, 

 though in the absence of ribs its homology with the rabbit's 

 sternum is very doubtful. The anterior prolongation con- 

 sists of episternum (cartilage) and omosternum (cartilage- 

 bone) ; the posterior, of mesosternum (cartilage-bone) and 

 xiphisternum (cartilage). 



Fig. 73. SHOULDER-GIRDLE AND ARM OF FBOO. 

 (After Howes.) 



