THE SKULL 



frontals than could the occipital, this presumably having had a dentate 

 type of suture. 



He considers that the simpler type of water-and-body force acting upon 

 the odontocete skull was complicated in mysticetes by the downward pull 

 exercised by the enlargement of the head for baleen armature, the down- 

 ward pull offered by the latter when the mouth is wide open for feeding, 

 and the upward pull at the back of the skull needed to counteract these 

 forces. He considers that the telescoping in this group has taken the 

 form largely of an overthrust of the occipital element from behind 

 forward chiefly because, like the present sea-lion, the occipital suture 

 of the mysticete stock was of the squamous type, over-riding the brain- 

 case with more ease than could the maxillary-premaxillary element which 

 presumably had a dentate type of suture with the frontal. 



In final analysis this theory of Miller's rests solely on the premise that 

 the only stimulus for the telescoping of the skull in whales of all types 

 has been the backward, or at times, oblique, pressure of the water through 

 which the animal moves. He advances as reasons for lack of telescoping 

 in the skulls of other aquatic mammals the facts that their heads are 

 relatively smaller, offering less resistance to the water, they are not held 

 so stiffly or uniformly pressed into the resisting element, and that they 

 all swim at lower speed. In explanation of the importance of the last 

 contention it may be mentioned that the resistance offered by water to 

 a body moving through it increases as the square of the velocity. Hence 

 the pressure against the head of a porpoise swimming at 30 miles per 

 hour would be 36 times as great as against a sea cow (did it have a head 

 of the same shape and size) moving at five miles per hour. 



There is certainly a definite stimulus supplied by strong, backward 

 water pressure which we would expect to find reflected in cranial details. 

 It is perhaps certain that no mammal that had not been accustomed to 

 moving through the water with speed for long ages could exhibit telescop- 

 ing of the skull in a form as perfected as we now find it in odontocetes. 

 We may therefore put this down as an essential stimulus. But I am very 

 loath to believe that this was of sole importance in producing telescoping. 

 We will therefore proceed to hunt for stimuli in this direction which 

 may also have been essential to the attainment of this condition, although 

 perhaps in themselves of insufficient strength to have produced it without 

 the aid of water resistance. 



It is clear that there is no need of great strength at the tip of the ceta- 

 cean rostrum. At least they get along very well without it, and its at- 

 tenuate form is permitted by the elimination of strong front teeth, the 



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