XIII 



PHYLUM CHORDATA 



631 



oect.tub 



isch 



jblkfor 



Skeleton of Cetacea.— In the Cetacea (Fig. 1148) the cervical 

 region {c&ro}j is al- 

 ways very short, and 

 the constituent verte- 

 brae are often com- 

 pletely fused to- 

 gether into a con- 

 tinuous bony mass, 

 or the atlas alone 

 may be separated 

 from the rest; but 

 sometimes all the 

 vertebrae are com- 

 plete and separate. 

 In the latter case 

 they have small 

 arches and long 

 transverse processes 

 consisting of two nar- 

 row bars with a wide 

 space between them. 

 The epiphyses are 

 very distinct discs 

 which often remain 

 separate from the 

 bodies up to a late period. The neural spines are well de- 

 veloped. The zygapopbyses are not well developed, and are 



absent in the posterior portioQ. In 

 the absence of hind-limbs there is 

 no sacral region. The caudal region 

 consists of numerous vertebrae be- 

 neath which, opposite the inter- 

 vertebral spaces, are a series of 

 chevron bones (chev.). 



In the Whale-bone Whales only 

 one pair of ribs articulates with 

 the sternum, and none articulate 

 with the bodies of the vertebrae, 

 but only with the transverse pro- 

 cesses. In the Toothed Whales 

 only a small number are connected 

 with the sternum, sometimes 

 through the intervention of inter- 

 mediate ribs, and a few of the 

 anterior only, in most cases, arti- 

 culate with the bodies of the vertebrae ; but in some a greater 



Fig. 1146. — Pelvis and sacrum of Armadillo (Dattypus sex- 

 cinctus). ac. acetabulum ; it, ilium ; isch. ischium ; obt.fov. 

 obturator foramen ; peci. tub. pectineal tubercle;^M6. pulais. 



Fig. mr.— Pes of Armadillo , 



iezeinctus). oat. astragalus ; col. cal 

 caneum ; cbd. cuboid ; ect. ecto-cunei' 

 form ; ent. ento-cuneiform ; vies. mesO' 

 cuneiform ; nav, navicular. 



