210 THE SKULL. [CHAP. 



the cribriform plate of the ordinary Mammal, though with 

 but few and small perforations ; (2) an anterior rod-like, 

 somewhat compressed, pointed prolongation from the lower 

 part of this plate, which extends forwards in the groove of 

 the vomer ( Vo) almost to the extremity of the rostrum, and 

 which in great part remains permanently cartilaginous. 

 This corresponds with the septal cartilage of the nose of 

 other Mammals, although owing to the altered position of 

 the nares it has here little relation with these passages. 



The cranial cavity is formed chiefly of the cerebral fossa, 

 the cerebellar fossa being relatively small, and the olfactory 

 fossa entirely wanting. 



The optic nerve passes out through a deep notch, some- 

 times a foramen, in the hinder border of the orbitosphenoid. 

 The alisphenoid is not perforated, the foramen rotundum 

 being confluent with the large sphenoidal fissure, and the 

 foramen ovale with a large infundibuliform opening between 

 the alisphenoid, parietal, exoccipital, basioccipital, and basi- 

 sphenoid, in the bottom of which is seen the inner surface 

 of the periotic (Per), which in the Cetacea makes no projec- 

 tion into the cerebral cavity. The anterior part of this 

 opening corresponds to the foramen lacerum medium with 

 the foramen ovale, the hinder part to the foramen lacerum 

 posterius. 1 The squamosal (,5V;) appears in the outer 

 boundary for a very small space, between the parietal and 

 the exoccipital. The condylar foramen pierces the ex- 

 occipital, near its anterior edge. The large or nearly 

 circular carotid canal has a peculiar position, passing 

 through the basisphenoid, near its middle, in a direction 

 from below upwards, forwards, and inwards. 



1 In the adult of the same species, the foramen ovale is separated 

 from the large opening common to the seventh and eighth pair of nerves 

 by a strong bony partition formed by the ossified tentorium cerebelli. 



