THE SKULL 



The mysticete mandible is profoundly modified by the necessity for 

 its enlargement and bowing to accommodate the baleen equipment. The 

 posterior processes are much reduced and the articulation with the skull 

 altered in that the articular ligaments are greatly spread so as to allow 

 a phenomonal amount of movement. The latter is further facilitated 

 by the lack of a true symphysis menti, the connection of the mandibular 

 tips being highly elastic; so that the mandible is perhaps capable of a 

 greater variety and degree of twisting, distortional movements than that 

 of any other mammal. This is doubtless of economic value in the se- 

 curing of food, and to facilitate the replacement of the baleen tips in 

 the eventuality that these become extruded from the mouth in some man- 

 ner. 



The development of the muscles of mastication in the Cetacea de- 

 serves brief mention. In the extinct squalodonts, with heavy teeth clearly 

 fitted for actively predaceous uses, the temporal muscles were quite well 

 developed, if we compare their fossae with the relative size of the brain- 

 case. In most living odontocetes, however, these fossae are much smaller ; 

 but it is interesting to note that they still occupy the area from zygomatic 

 process of the squamosal to the frontal border, as is usual in terrestrial 

 carnivores. In other words, the reduction in size of the temporal muscles 

 has kept pace with lateral displacement of the parietals (in Tursiops for 

 instance) . This may or may not have any real significance. It is well 

 known (see, for instance, Anthony, 1903), however, that mammals of 

 small brain capacity are very apt to have powerful temporals reaching 

 the sagittal crest, which may be very high, and that as the brain becomes 

 larger and more highly specialized, the tendency will be for a definite 

 reduction in size of the temporal fossae. The latter condition is probably 

 not primarily a result of the increase in brain size, but is a reflection of 

 the fact that to all intents a mammal to which great power of the dental 

 armature (to which condition large temporal muscles are necessary) 

 and consequent development of the anterior face, is critically requisite, 

 is hindered in the development at the same time of a large brain. Again, 

 this may or may not be of significance in the case of odontocetes. 



Following the reduction in size and masticatory importance of the 

 teeth the masseter muscles of at least some odontocetes are decadent. 

 In fact they may not have any definite attachment to the skull at all 

 (Neomeris) and but a very slight one to the mandible. But they were 

 probably much better developed in the extinct porpoises with phe- 

 nomenally long beaks. 



[119] 



