XIII 



PHYLUM CHORDATA 



499 



.peel, tub 



b&for 



Skeleton of Cetacea. In the Cetacea (Fig. 1079) the cervical 



region (cert?.) is always 



very short, and the 



constituent vertebrae 



are often completely 



fused together into 



a continuous bony 



mass, or the atlas 



alone may be separ- 

 ated from the rest ; 



but sometimes all the 



vertebra are com- 

 plete and separate. 



In the latter case 



they have small 



arches and long trans- 

 verse processes con- 

 sisting of two narrow 



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 developed. The zygapo- 



physes are not well developed, and are absent in the posterior 



portion. In the absence of hind 

 limbs there is no sacral region. The 

 caudal region consists of numerous 

 vertebrae beneath which, opposite 

 the intervertebral spaces, are a 

 series of chevron bones (ckev.). 



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 the anterior few 

 only, in most cases, articulate with 

 the bodies of the vertebras ; but in 



some a greater number articulate with both transverse processes 



and bodies by distinct tubercles and heads. 



K K 2 



FIG. 1077. Pelvis and sacrum of Armadillo (Dasypus sex- 

 cinctus). ac. acetabulum ; il. ilium ; isch. ischiutn ; obt. for. 

 obturator foramen ; pect. tub. pectineal tubercle ; pub. pubis. 



cat 



cist 



FIG. 1078. Pes of Armadillo (Dasypus 

 sexcinctus). ast. astragalus ; cat. cal- 

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

 form ; ent. ento-cuneiform ; mes. meso- 

 cuneiform ; nav. navicular. 



