THE ORDER CETACEA. 1 1 i ) 



whalebone is inserted. At the posterior part of this 

 surface, and between the mastoid processes,* the two 

 bones containing the organ of hearing, denominated the 

 petrous, or, as I term them, the acoustic bones, are 

 placed. In the interior there is a nervous pulp, in which 

 the sense of hearing is supposed to reside. 



The posterior surface or base of the skull is of a semi- 

 circular form, with two large alee or wings on its sides, 

 at the bottom of the pterygoid or wing-like processes of 

 the sphenoidal or wedge-like bone. There are the hu- 

 mular or hook-like processes, to which the pharynx or 

 upper part of the gullet is attached. The great occipital 

 foramen or orifice in the back of the head for the 

 passage of the spinal marrow from the brain, is situated a 

 little above the preceding. On each side of this fora- 

 men or orifice there are the semilunar condyles or knobs 

 of the occipital (hind head) bone, which are articulated 

 with the atlas or the first bone of the neck as in the 

 other mammalia. The remainder of this portion of the 

 skull is occupied by the greater part of the occipital and 

 the mastoid processes. 



The lateral surfaces are formed by the end of the pala- 

 tine bones anteriorly ; the zygomatic fossa or cavity and 

 its arch posteriorly. This surface embraces portions of 

 the temporal, occipital, and the sphenoidal bones. 



On viewing the head vertically, we find several inter- 

 esting peculiarities; the occipital bone measures more 

 than three feet in thickness, and is very spongy in its 

 texture, whilst the external table is at the same time 

 extremely thin ; consequently the specific gravity must 

 be very little, notwithstanding its immense size. The 

 nasal cavities are very largely developed, and in the 



* Processes of the temporal boue, shaped like the nipple of the human 

 female breast. 



