THE CETACEA. 393 



enlargement of tlie upper jaw taking place in the region 

 whicli lies in front of the nasal apertiu-e. The basis cranii, 

 as a whole, is remarkably broad, and its upper surface 

 concave from before backwards, the sella turcica being very 

 slightly indicated. The parietal bones are comparatively 

 small, and do not meet in a sagittal suture, as they do in 

 other Mammalia ; the supraoccipital, with an interparital 

 bone, being interposed between them, and extending for- 

 wards so as to unite with the frontals. Each frontal 

 bone is prodiiced outwards into a great bony plate which 

 covers the orbit. The squamosal bone sends a very large 

 and stout zygomatic process forwards to meet this supi-a- 

 orbital prolongation of the frontal. The proper jugal 

 bone, on the other hand, which bounds the orbit below, 

 is exceedingly slender. The very large maxilla extends 

 backwards and outwards in contact with the frontal, or 

 even overlapping the greater part of its surface; and it 

 stretches forwards to very near the anterior end of the 

 snout, so that almost the whole of the gape is bounded by 

 the maxilla. 



The premaxillse, on the other hand, thoi^gh very long, 

 inasmuch as they occupy the whole length of the jaw in the 

 middle line, from the anterior nasal aperture to the end of 

 the snout, are almost entirely excluded from the gape. 



The nasal bones are always short; and, sometimes, are 

 mere bony tuberosities united with the frontal bones behind 

 the anterior nasal aperture. The turbinal bones are almost 

 always rudimentary, and the nasal passages are nearly ver- 

 tical, in conseqiience, for the most part, of the I'udimen- 

 tary condition and shortness of the nasal bones. 



The periotic bones are loosely connected with the squa- 

 mosal and tympanic, and are usually united with the other 

 bones of the skull only by cartilage, so that they fall out 

 very readily in the diy skull. The tympanic bones are 

 commonly of very considerable size, thick and scroll- 

 shaped. 



The lower jaw has hardly any coronoid process, and its 

 ramus has no perpendicular portion, the condyle beinw 



