MOUTH AND NOSE 



from a common ancestry, more pronounced differences developed each 

 in its own particular way as specialization increased. It is thus easily 

 seen that the narial musculature of a beaked porpoise with rather low 

 forehead, such as Tursiops, should be considerably different from that 

 of a nonbeaked form with large frontal bulge, such as Globiocephala 

 (see fig. 10). Of the first type I have examined only Tursiops, and of 

 the second, Monodon and Neomeris, and the last was too hardened to 

 be satisfactory. In this only did I attempt to dissect the facial muscu- 

 lature, for in the others this was done by Ernst Huber. I will there- 

 fore not go into precise details but will discuss only the generalities of 

 this feature. 



In the majority of odontocetes, then, the external nares take the form 

 of a single crescentric orifice. Within this, at a distance varying with the 

 genus or species, the passage is divided by a membranous partition into 

 two. In this, as well as in mysticetes, the supracranial part of the nasal 

 passages is practically vertical or slopes gently forward as it approaches 

 the surface. But between the skull and the orifice in odontocetes there 

 is a system of diverging diverticula or membranous folds (see descrip- 

 tion of Neomeris, Howell, 1927). These apparently vary with the spe- 

 cies, or even with the individual, but as I understand their underlying 

 principle they had better be described as two different parts of the nos- 

 trils. Lying forward of the bony nares and in contact with the pre- 

 maxillae in a slight hollow of these bones, the extent of which can be 

 determined upon the skull, is a diverticulum of each nostril which may be 

 designated the premaxillary diverticula. These and the supracranial part 

 of the nostrils proper describe an angle of, say, 90 degrees or less. 

 Within this angle the tissue is very soft because of the soft fat of 

 which it is largely composed. At the apex of the angle this soft tissue 

 fits over the bony narial openings, effectively sealing them, especially 

 when there is any pressure from without. When the animal wishes to 

 take a breath the soft tissue, acting as a plug, is drawn forward by mus- 

 cular action in a way that is greatly facilitated by the premaxillary di- 

 verticula. This action is strongly suggested by conditions in an adult 

 narwhal (Monodon) the entire head of which H. C. Raven had sawn 

 lengthwise in thin sections. When examining figure 15, however, it 

 should be clearly understood that the sketch is only roughly diagrammatic 

 and the degree of expansion of the deeper part of the passages and 

 diverticula is unknown. Neither is it meant to imply by the above state- 

 ments that these deep parts are always kept closed between breaths. Per- 

 haps the complete sealing of the entire mechanism is indulged in only 

 at some depth. 



[97] 



