118 



ON THE VERTEBRATE SKULL. 



posterior basi-cranial (BO, B8, PS), which forms the centre of 

 the floor of the proper cranial cavity; and an anterior, hasi- 

 facial (Eth., To.), which constitutes the axis of the front part of 

 the face. 



Fig. 51. 



Fig, 51. — Front view of the skull, the halves of which are shown in Figs. 48 and 49. — 

 N, nasal chamber ; Or, orbit. The nasal bones are removed, and so much of the 

 upper and lower jaws as is necessary to show the permanent teeth. 



Three pairs of chambers, destined for the lodgment of the 

 organs of the higher senses, are placed symmetrically upon 

 each side of the double bony box thus described. Of these, 

 two pair are best seen in a front view of the skull (Fig. 51), the 

 inner pair being the olfactory, or nasal chambers (X), the outer 

 pair, the orbits (Or). The other pair are better displayed in 

 the transverse sections, Fig. 48 and Fig. 49, and are formed by 

 the temporal bones of anatomists (T, Tl), and especially by the 

 petrous and mastoid portions of those bones. 



There is an obvious difference between the relations of these 

 3ensory chambers to the contained sensory organ, in two of 



