XIII 



PHYLUM CliORDATA 



531 



Skeleton of Cetacea. 



region (cerv.) is al- 

 ways very short, and 

 the constituent verte- 

 bni; 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 



-In the Cetacea (Fig. 1148) the cervical 



ai: - 



^,pect.tub 



ccc 



tsch 



separate from the 



bodies up to a late period. 



veloped. The zygapophyses 



Pig. 1146. — Pelvis and sacrum of Armadillo {Da^ypva sex- 

 rinctns). ac. acetabulum ; il. Ilium ; itcli. iseliiuni ; oht.for. 

 obturator fonuiien; pect. tub. pectineal t\\\>bxc\e.;pub. pubis. 



Fig. 1147.— Pes of Armadillo (Ddsypus 

 sexcinctus). ast. astragalus ; cal. cal- 

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

 forin ; ent. ento-ouneiform ; jjim. meso- 

 cunciform ; nav. navicular. 



culate with the bodies of 



The neural spines are well de- 

 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 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 vertebrse, 

 but only with the transverse pro- 

 cesses. In the Toothed Whales 

 number are connected 

 sternum, sometimes 

 intervention of inter- 

 and a few of the 

 most cases, arti- 

 in some a greater 



only a small 

 with the 

 through the 

 mediate ribs 



anterior only, in 

 the vertebr* ; but 



