THE SKULL 



with them the main trunk of the facial nerve, which now turns abruptly 

 backward over a groove in the maxilla and lachrymal at the base of the 

 rostrum and so to the dorsal surface. A like condition obtains in the 

 case of the usual anterior opening of the infraorbital nerve of the maxil- 

 lary branch of the trigeminal, the infraorbital foramen having been 

 forced first dorsad and then caudad, where the nerve now emerges in 

 separate branches from several foramina, which may be located directly 

 above the eye {Tursiops) and even within the bony narial orifice. 

 Whether or not this actually be the case it appears superficially very 

 much as though the posterior extension of the premaxillaries and the 

 expansion caudad and laterad of the maxillae had been stimulated to 

 this action by the migration in these directions of the facial muscles 

 which are so firmly attached to these bones; — that the attachments of 

 these muscles had not shifted from one bone to another but had dragged 

 the bones with them, just as anterior migration of the occipital muscles 

 alters conformation of the occiput. And that the more circumscribed 

 area which these narial muscles needed in attachment to the frontals 

 had permitted all but a narrow border of these to be covered by the 

 maxillae. At any rate this excessive migration of the nostrils has had 

 a profoundly stimulating effect upon osseous conformation. This is 

 beyond question. 



The mysticetes indicate an entirely different state of affairs. There is 

 no backward pressure of water against the anterior wall of the brain- 

 case, save as applied through the rostral tip, and there has been no oc- 

 casion to build up a thickened or laminated bony wall for its proper 

 resistance, nor is there an adipose cushion in this region. Unlike odon- 

 tocetes the baleen equipment has retained considerable growth-stimulus 

 in the rostrum proper, and the nostrils and their musculature have not 

 been forced as far backward against the braincase as they could go. On 

 the contrary the bony nares are more nearly comparable to the usual 

 mammalian condition. And most important of all, there has not been 

 such a pronounced migration backward of the narial musculature, and 

 the requirements in this respect are not such as to necessitate any great 

 broadening out of bony elements to accommodate a pyramid of muscles as 

 broad as any part of the skull, for in mysticetes the intertemporal region 

 is quite narrow. 



Kellogg (1928) considers that the mysticete maxillae cannot over- 

 spread the braincase because the posterior part straddles the supraorbital 

 processes of the frontals, and he presumably accepts this as a fundamental 

 reason why these whales do not exhibit more telescoping at the base of 

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