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 cachelot whale {Physeter~}, from Huxley. AS, 

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

 cipital; Eth, ethmoid; Fr, frontal; Ju, 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; Sy, 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 



