MOUTH AND NOSE 



limbs, the head and anterior part of the neck do not constitute such a 

 critical part of the natatory equipment. Hence the head may be thrust 

 moderately in any direction without disturbing equilibrium providing 

 the hinder end acts in compensation. Furthermore the mouth is used 

 to a considerable extent for breathing, and we cannot be sure that 

 there is any really marked stimulus experienced for the retraction of 

 the nares. 



ADIPOSE CUSHION 



Because of a complex of reasons, chief among which are doubtless 

 the size and breadth of the head, and feeding habits, the speedy balaenop- 

 terid whales carry the flattish dorsum of the head parallel with the body 

 axis, so that there is the minimum of cephalic resistance offered to the 

 water. The slower Rhachianectes and balaenid whales have a down- 

 ward-curving rostrum, but the base of the rostrum and posterior part 

 of the head are carried parallel with the body axis also. In these there 

 is no adipose cushion in the frontal region, unless the "bonnet" of 

 Eubalaena, consisting of a raised, warty area upon the anterior rostrum, 

 could be considered as the beginning of such a structure. 



All odontocetes, without exception I believe, have some sort of recog- 

 nizable adipose cushion equipment upon the forehead. In these whales 

 the outline of the head from snout to vertex is never a straight line 

 that can be carried parallel to the body axis so that the only resistance 

 to the water is offered by the tip of the snout. The latter is always 

 carried slightly depressed. In the beaked porpoises (as Tur stops and 

 Delphinus, fig. 10), the dorsal outline is concave where the rostrum 

 meets the cerebral part of the head, while in the short-snouted sorts the 

 forehead is protuberant, but in all, the frontal region is anteriorly pre- 

 sented so that it receives the impact of the water during swimming. 

 This, being the front of the braincase, is a region of rather critical 

 delicacy, and it might be expected to respond to this stimulus by building 

 up some sort of protective buffer or shock-absorber: but the subject 

 cannot be abandoned with any such simple statement. 



The adipose cushion in the majority of odontocetes is a thick pad of 

 soft, elastic tissue upon the forehead in front of, and even partly sur- 

 rounding, the blowhole. It need not be sharply defined, but the fibrous 

 tissue and soft fat of which it is composed is surrounded and to some 

 degree penetrated by the facial muscles which converge to or toward the 

 blowhole. Directly anterior to the blowhole it is composed of pure, 

 soft fat that oozes oil when transected. This fat is not the same as 



[103] 



