24 



SACRUM AND CAUDAL SERIES 



number of vertebrae fused together and supported by the pelvic 

 girdle is characteristic of the mammals, but is not found in the 

 Cetacea and the Sirenia, where functional hind-limbs are wanting. 

 Strictly speaking, the sacrum is limited to the two or three 

 vertebrae whose expanded transverse processes meet the ilia. 

 But to these are or may be added a variable number of vertebrae 

 withdrawn from both the lumbar and the caudal series, which 



a^et 



isch 



pt/,b 



Fig. 12. — Lepxis amicuhcs. Innomin- 

 ate bones and sacrum, ventral aspect. 

 acet, Acetabulum ; il, ilium ; isch, 

 ischium ; oht, obtiirator foramen ; 

 pub, pubis ; .'.ffcr, sacrum ; si/, sym- 

 pbysis. (From Parker, and Haswell's 

 Zoolofftj.) 



Fig. 13. — Anterior surface of fourth 

 caudal vertebra of Porpoise (Pho- 

 coena communis), x i. /t, Chevron 

 bone ; m, metapophysis ; s, spin- 

 ous process ; t, transverse process. 

 (From Flower's Osteology.) 



unite with each other to form the massive piece of bone which 

 constitutes the sacrum of the adult. 



The caudal vertebrae complete the series. They begin in as 

 fully developed a condition as the luinbars, with well-marked 

 transverse processes, etc. ; but they end as no more than 

 centra, from which sometimes tiny outgrowths represent in 

 a rudimentary way the neural arches, etc. Very often the 

 caudal vertebrae are furnished with ventral, generally V-shaped, 

 appendages, the chevron bones or intercentra.^ These are 



^ Intercentra are but rarely met with anterior to the caudal series. Mr. Parsons 

 has, however, recorded their occurrence in the lumbar vertebrae of Atherura. 



