424 



ANATOMY OF VERTEBRATES. 



next with the upper end of the premaxillary, and for the rest of 

 its extent with the maxillary bone, which is continued onward to 

 form the antorbital process. 



In the mature Mysticete Whale, of which a side view of the 

 skull (now in the British Museum) is given in fig. 285, the maxil- 

 laries, 21, are disposed each like an expanded arch along the 

 outside of the coextended premaxillaries, 22 ; their inferior surface 

 has two facets separated by a longitudinal ridge, to the sides of 

 which the plates of baleen are attached. The premaxillaries are 

 compressecl and diverge from each other posteriorly to form the 

 long oval outlet of the nostrils, completed behind by the nasals, 

 which are elongate, as in the Zeuglodon ceto'ides : the frontals, e, 

 extend outward to form the roof, 1 1, of the small orbit, 0; and there- 

 with is coextended the back part of the maxillary, 21': a small ma- 

 2gg lar, fig. 159, 26, is articulated 



to the lacrymal, 73, the maxil- 

 lary, 21, and the squamosal, 27; 

 the most expanded part of which, 

 fig. 285, 27, forms the articula- 

 tion for the mandible, 29-32. 

 The superoccipital, 3, inclines 

 forward, as it rises, and forms 

 almost the whole upper part of 

 the cranium. The coalesced pre- 

 frontals are perforated by the ol- 

 factory nerves. The presphenoid 

 is sheathed in the hind part of 

 the canaliculate vomer, i3,which 

 extends far forward along the 

 middle of the roof of the mouth. 

 Each mandibular ramus arches 

 outward and forward from the 

 slightly-raised condyle, 29, to the 

 short, ligamentous symphysis, 

 32 : it is compressed and subtrenchant at both upper and lower 

 margins : a coronoid ridge is feebly marked ; there is no ascend- 

 ing ramus. The skull of the whale is more symmetrical than 

 that of toothed Cetacea. 



In the section of DeljjliinidcB to which the Grampuses and 

 Porpoises belong {PhoccRiia, Cuv.), the facial bears a less pro- 

 portion to the cranial part of the skull : the latter is broad, ele- 

 vated, and convex posteriorly. The superoccipital, fig. 286, 3, 

 forms the transverse crest dividing the hinder from the upper 



Skull of a Grampus {Phocccna fjlubiceps). 



