INTRODUCTION. 87 



the vestibulum, and by the other with the tym- 

 panum. The cranium, or skull, may be sub-divided 

 into three compartments, the anterior containing the 

 two frontal bones and the aathmoid ; the central por- 

 tion being the parietal bones and sphenoid, and the 

 hinder part composed of the occipital bone ; between 

 the occipital, the parietals and the sphenoid are 

 placed the temporal bones, of which a part belongs 

 to the face. 



The face is essentially composed of the two 

 maxillary bones, containing betwixt them the canal 

 of the nostrils : upon these are the two inter- 

 maxillaries, and behind the two palate bones ; be- 

 tween them descends the single blade of the aethmoid, 

 named vomer, and upon the entrances of the nasal 

 canal are placed the bones, properly termed nasal. 

 To the external parts of the entrance adhere the in- 

 ferior turbinated bones, but the superior turbinated 

 bones belong to the aethmoid, and are placed behind 

 and above. This general structure of the nasal ap- 

 paratus is not found in cetacea ; the two canals cor- 

 responding to the nostrils pierce the head vertically, 

 admitting the air to and from the lungs when the 

 head is nearly entirely immersed in water, and ex- 

 pelling the liquid which may come in at the mouth. 



The jugal, or cheek bones, unite on each side the 

 maxillary, to the temporal bones, and often to the 

 frontal, and the lachrymals occupy the internal angle 

 of the orbits, extending sometimes over a part of the 

 cheeks. 



