THE SKULL 



of the occipital. Some of the more peculiar types of ziphioid whales 

 also have an occipital that is almost vertical: but in odontocetes of the 

 porpoise sort there is marked forward inclination of the occipital plane 

 (discussed later). This is definitely rounded and the supero-medial 

 part extends to meet the facial plane. This crowding has forced the 

 parietals far laterad. The restricted temporal fossae project backward to 

 indent the occipital expanse, and the lower part of the exoccipitals and 

 lateral part of the basioccipital are projected into marked processes. The 

 bony border resulting is not continuous but has a deep fissure for the 

 jugular vein and nerves IX, X, and XI (glossopharyngeal, vagus and 

 spinal accessory), with the condyloid foramen (for the hypoglossal 

 nerve) upon its border. Upon this falcate border of the basi- and exoc- 

 cipitals is inserted the great dorsal scalene muscle, which is probably for 

 the purpose of providing static strength in the same way that the rectus 

 capitis superior is so used upon the opposite side of the neck, but it 

 doubtless also assists in swimming motions. At any rate this falcate 

 border is not present in Mysticeti, the downward motions of whose heads 

 are (presumably) largely governed by the specialized gular musculature, 

 which has leverage clear from the tip of the mandible. 



The occipital condyles of the Cetacea are massive but are not any 

 broader in relation to the width of the skull than in many terrestrial 

 carnivores. 



On the whole the cetacean brain is of a very high type — quite extra- 

 ordinarily so when we consider that as far as can be judged members of 

 this order have less need for such equipment than almost any other 

 mammal. It is perfectly apparent upon inspection of skulls that the 

 brain capacity of an ordinary porpoise such as Tursiops is relatively con- 

 siderably greater than in a large baleen whale. But this may be merely 

 in conformity with Haller's law, which is to the effect that in related 

 animals the relative size of the brain is greater in the smaller sorts, 

 and that endocranial capacity decreases as size increases. Dubois (1924) 

 has stated that volume of brain in such comparable material ("species 

 of equal organization") increases as the 5/9 power of the body weight, 

 and that in mysticetes this cephalic index (not actual capacity of the 

 brain case) is only one-third of what it is in porpoises. It is therefore 

 difficult to determine whether there is actually a difference in the endo- 

 cranial capacity between equal-sized representatives of the two cetacean 

 groups, for the skulls of the larger toothed whales are curiously distorted 

 in some respects and the smallest mysticetes are depauperate and not 

 representative of the group. At any rate, regardless of this point, the 



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