XII.] 



GET ACE A. 



21 I 



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 



Na 



Fr 



FIG. 65. A section of the skull of a young Dolphin (Globicepkalus vielas), \. PM.\: 

 premaxilla ; MX maxilla ; MR ossified portion of the mesethmoid ; an anterior 

 nares ; Na nasal ; IP interparietal ; Fr frontal ; Pa parietal ; SO supraoccipital ; 

 ExO exoccipital ; BO basioccipital ; Sq squamosal ; /Vrperiotic ; AS alisphenoid; 

 PS presphenoid ; Pt pterygoid ; pu posterior nares ; PI palatine ; Vo vomer ; 

 ^ symphysis of mandible ; id inferior dental canal ; cp cjron jid process ; cd con- 

 dyle ; a angle ; sh stylohyal ; bh 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 



p 2 



