350 



NASAL BONES 



phins and, especially, Physeter. This asymmetry affects parti- 

 cularly the premaxillae, the maxillae, and the nasals. The 

 base of the skull is symmetrical. The Whale's skull has very 

 long premaxillae which, however, do not, except in the extinct 



PMX 



Fig. 184. — Under surface, of the craniuiii of a young Caa'ing Whale [Glohicephalus 

 melas). ■k\. A 8, Alisphenoid ; BO, basioccipital ; cf, condylar foramen ; ExO, 

 exoccipital ; Fr, supra-orbital process of frontal ; gf, glenoid fossa of squamosal ; 

 Ma, body of malar ; Mx, maxilla ; OS, orljitosphenoid ; Per, posterior (mastoid) 

 process of periotic ; /-■/, palatine ; PMx, premaxilla ; I't, pterygoid ; Sq, squamosal ; 

 tg, deep groove on squamosal for meatus auditorius externus, leading to tympanic 

 cavity ; Tg, tympanic ; Vo, vomer ; ZM, zygomatic process of malar, (From 

 Flower's Osteologg.) 



Zeuglodonts, bear any teeth. The nasal bones, whether sym- 

 metrical or the reverse, are very small in existing Whales, 

 which arrangement, together with the long and broad maxillary 

 bones, removes the anterior nostrils, the blow -hole, far back- 

 wards. The roof of the skull is not at all formed by the 

 parietals externally. These bones form a portion of the side 

 of the cranium, l)ut are replaced or covered by the enormously- 



