220 THE SKULL, [CHAP. 



frontals, which are of considerable antero-posterior thick 

 ness at this part (see Fig. 67, Fr\ and also by moderately- 

 developed nasals (Na\ meeting by a flattened surface in 

 the middle line. The nares are still near the most elevated 

 part of the head, and the premaxillae and maxillae, with the 

 vomer and mesethmoid cartilage, are produced in front of 

 them into a long tapering rostrum, narrow, compressed, and 

 much arched in the Right Whales {Balcena); broader, de- 

 pressed, and nearly straight in the Rorquals (Bahenoptera). 



An essential difference between the Whales and the 

 Dolphins is the presence in the former of an olfactory organ 

 of the same type as in other Mammals, though in a compara- 

 tively rudimentary condition. In the skull of an adult Green- 

 land Whale (Balcena mysticetus], the olfactory fossa of the 

 cerebral cavity is eight and a-half inches in length, scarcely 

 more than half an inch high, and one and a-half inch 

 wide. It runs forward from the anterior part of the floor of 

 the cerebral fossa, through the great mass of bone formed by 

 the union of the frontal, mesethmoid and presphenoid. In 

 front it divides into two compartments, each somewhat oval 

 and dilated, with a concave floor about an inch in extent 

 in either direction, perforated with foramina. This floor is 

 the cribriform plate. In the hinder wall of the great narial 

 passage is a narrow vertical slit, twelve inches in length, 

 very near the middle line ; this is the opening of the 

 olfactory chamber of the nasal cavity, which is bounded 

 by the under surface of the cribriform plate above, by the 

 flat mesethmoid on the inner side, and has its outer wall 

 raised into several longitudinal elevations of very simple 

 character, representing the ethmoturbinal bones. 



In the Rorquals (Balcenoptera) the olfactory fossa is less 

 elongated, the foramina of the cribriform plate larger and 

 more numerous, and the ethmoturbinals better developed. 



