XII.] 



CETACEA. 



211 



The bones forming the walls of the cranial cavity are dis- 

 posed in a very remarkable manner. The occipital surface 

 is of great size, and slopes upwards and forwards. The 

 foramen magnum is large, and looks directly backwards ; its 



Pa 

 SO 



ExO 



II 



r<f 



FIG. 65. A section of the skull of a young Dolphin (Globictfikalui nielas), |. PMx 

 premaxilla ; MX m.ixill.i ; ME ossified portion of the mesethmoid ; an anterior 

 nares ; t<ln nasal ; //' interparietal ; /> frontal ; Pa parietal ; SO supraoccipital ; 

 EjcO exoccipital ; KO basioccipital : Sq squamosal ; Per periotic ; AS alisphenoid; 

 PS presphenoid ; Pt pterygoid ; />n posterior nares ; PI palatine ; Vo vomer : 

 * symphysis of mandible ; id inferior dental canal ; ef cjronjid process ; erf con - 

 dyle ; a angle ; sh stylohyal ; bk basihyal ; th thyrohyaL 



lower lateral margins are bounded by large oval condyles, 

 which meet in the middle line below, and are formed by 

 the exoccipitals, with a small portion of the basioccipital. 

 Above the foramen, the immense supraoccipital (SO), with 

 which an interparietal (IP) is ankylosed, extends forwards 



