MOUTH AND NOSE 



having to do with facial expression, while in the whale all these muscles 

 are subservient to the single purpose of opening the blowhole. Such 

 as cannot readily lend themselves to this use have become virtually non- 

 functional. It is therefore of small wonder that we find the nasal 

 mechanism as perfected as it now is in the odontocetes. Furthermore, 

 in view of the bronchial conditions as reported by Wislocki it is neces- 

 sary that we free our minds of the assumption that a special provision 

 for the purpose of retaining air under great pressure is situated in the 

 blowhole. Nor is a complicated contrivance for excluding water essential. 

 The external area of the closed blowhole is small and it has been a simple 

 process for this to acquire such a form that the greater the pressure the 

 tighter is automatic closure. 



Precranial narial conditions in the Cetacea are really of three sorts, the 

 most simple being in the Mysticeti, a more involved situation in most 

 Odontoceti, and a remarkably complicated one in the Physeteridae and 

 Kogidae. In mysticetes the nostrils are in the form of two slits running 

 in a sagittal direction (see fig. 13) , but converging to form a rather steep- 

 sided V with angle pointing forward. They do not actually join, how- 

 ever. Along the margin of each slit is a raised area, the elevation being 

 slight along the medial margin and considerably higher along the lateral. 

 To the touch this region is, like the rest of the body, tough and elastic. 

 I have run my arm to above the elbow down one nostril and found that 

 there was decided, though not heavy, pressure upon my arm for per- 

 haps one foot below the surface, and as my arm was withdrawn, the 

 elasticity of the tissue closed the passage completely. This involuntary 

 closure may likely be assisted, does the need arise, by voluntary tension 

 at both ends of the nasal slit, and by a downward contraction from the 

 surface. But the conditions are such that the greater the surface pressure 

 the more securely do the nostrils close, and I regard it as unlikely that 

 the need ever arises for voluntary closing action in order to exclude sea 

 water. In mysticetes there are no widely divergent diverticula. There 

 is well known to be a "subcircular diverticulum from the dorsal wall 

 of the respiratory passage," as stated by Schulte (1916), marking the 

 olfactory region, and a "spritzsac" along the anterior wall, but from 

 published descriptions I am unable exactly to envision the conditions. 

 By manual investigation within the passages of a fresh adult I could 

 not discover any true diverticula but only a slight folding and wrinkling 

 of the mucosa rostrad and to a lesser extent laterad. Schulte considered 

 the arrangement of this to be such as to aid closure when pressure is 

 supplied from without. 



[95] 



