MAMMALS. 



407 



The teeth in existing species are homodont and monophyo- 

 dont, and never pierce the gums in the mystacocetes. In the 

 fossils there is evidence of descent from heterodont ancestors. 



Pmx 



Pmx 



FIG. 374. Skull of foetal cachalot whale (Physeter}, from Huxley. AS r 

 alisphenoid ; Au, auditory region; BO, basioccipital ; BS, basisphenoid ; O, exoc- 

 cipital; Eth, ethmoid; Fr, frontal; fu, jugal (displaced in the side view from its 

 connection with the squamosal) ; MX, maxillary; N, external nares; Pa, parietal; 

 PI, palatine; Pmx, premaxillary; SO, supraoccipital; S</, squamosal; Vo, vomer. 



The number varies greatly. The stomach (p. 367) is several 

 chambered, the intestine is comparatively simple, a caecum being 

 present in some species. The liver has four lobes, and no gall 



