XIII 



PHYLUM CHORDATA 



499 



,pecl.tub 



ac 



cut 



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

 region (cem) is always 

 very short, and the 

 constituent vertebra? 

 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 

 vertebrae 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 clistinct 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 

 vertebra? beneath which, opposite 

 the intervertebral spaces, are a 

 series of chevron bones (chev.). 



In the Whale-bone Whales only 

 one pair of ribs articulates 4 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 vertebra? ; 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 (Dv.siqms sex- 

 cinctus). ac. acetabulum ; il. ilium ; isch. ischium ; oU. for. 

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



oa.1 



cist 



FIG. 1078. Pes of Armadillo (Dasypus 

 sexcinctus). axt. astragalus ; cal. cal- 

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

 form ; ent. ento-cuneiform ; me*, meso- 

 cuneiform ; nav. navicular. 





