The lumbar vertebrae, which follow the dorsal, vary greatly in number. There are as few as two in the whale _Neobalaena_, as many as seventeen in _Tursiops_; this group, the Cetacea, contains the extremes. Nine lumbars are found in the Lemurs _Indris_ and _Loris_. As a rule the number of lumbars is to some extent dependent upon that of the dorsals. It often happens that the number of thoraco-lumbar vertebrae is constant for a given group. Thus the Artiodactyles have nineteen of these vertebrae, and the Perissodactyles as a rule twenty-three. A greater number of dorsals implies a smaller number of lumbars, and of course _vice versa_. The existence of a sacral region formed of a {24} 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 But to these are or may be added a variable number of vertebrae withdrawn from both the lumbar and the caudal series, which unite with each other to form the massive piece of bone which constitutes the sacrum of the adult. [Illustration] [Illustration] FIG. 12.--_Lepus cuniculus_. Innominate bones and sacrum, ventral aspect. _acet_, Acetabulum; _il_, ilium; _isch_, ischium; _obt_, obturator foramen; pub, pubis; _sacr_, sacrum; _sy_, symphysis. (From Parker and Haswell's _Zoology_.) FIG. 13.--Anterior surface of fourth caudal vertebra of Porpoise (_Phocoena communis_), x 1/2. _h_, Chevron bone; _m_, metapophysis; _s_, spinous process; _t_, transverse process. (From Flower's _Osteology_.) The caudal vertebrae complete the series. They begin in as fully developed a condition as the lumbars, 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 [12]-shaped, appendages, the chevron bones or intercentra.[13] These are {25} particularly conspicuous in the Whales and in the Edentates. In the former group the occurrence of the first intercentrum serves to mark the separation of the caudal from the lumbar series. The number of caudals varies from three in Man--and those quite rudimentary--to nearly fifty in _Manis macrura_ and _Microgale longicaudata_. [Illustration] FIG. 14.--Lateral view of skull of a Dog. _C.occ_, Occipital condyle; _F_, frontal; _F.inf_, infra-orbital foramen; _Jg_, jugal; _Jm_, premaxilla; _L_, lachrymal; _M_, maxilla; _Maud_, external auditory meatus; _Md_, mandible; _N_, nasal; _P_, parietal; _Pal_, palatine; _Pjt_, process of squamosal; _Pt_, pterygoid; _Sph_, alisphenoid; _Sq_, squamosal; _Sq.occ_, supraoccipital; _T_, tympanic. (From Wiedersheim's _Comparative Anatomy_.)