462 THE VERTEBRATE SKELETON. 



important distinctions from the Odontoceti. The maxillae are 

 large, but do not extend back to cover the frontals as in the 

 Odontoceti. The zygomatic process of the squamosal is very 

 large. The mandibular rami are riot compressed, but are 

 rounded and arched outwards, and never meet in a long 

 symphysis. 



ODONTOCETI. The skull departs widely from the ordinary 

 mammalian type. The following description will apply to any 

 of the following genera of the Delphinidae, Phocaena, Globi- 

 cephalus, Lagenorhynchus, Delphinus, Tursiops, Proddphinus, 

 Sotalia. 



The upper surface of the skull is more or less asymmetrical. 

 The cerebral cavity is high, short and broad ; and formed mainly 

 by the cerebral fossa, the olfactory fossa being entirely absent. 

 The supra-occipital (fig. 93, 3) is very large, and forms much 

 of the posterior part of the roof of the skull. It has the 

 interparietal (fig. 93, 7) fused with it, and completely separates 

 the two parietals. The frontal (tig. 93, 10)- is large and late- 

 rally expanded, forming the roof of the orbit, but is almost 

 completely covered by an extension of the maxilla. The 

 zygomatic arch is very slender, and is mainly formed by a 

 rod-like process from the jugal (fig. 93, 15), the zygomatic 

 process of the squamosal being short and stout. 



The nasal passages are peculiarly modified, instead of 

 passing horizontally forwards above the roof of the mouth, 

 they pass upwards and even somewhat backwards towards 

 the top of the skull (fig. 93, 23). They are bounded laterally 

 by two processes from the premaxillae, the left of which is 

 shorter than the right. The nasal cavities are narrow and 

 without turbinals and the nasals (fig. 93, 19) are almost as 

 much reduced as in Sireriia. 



In front of the nasal openings the face is prolonged as a 

 narrow beak or rostrum of varying length, formed by the 

 maxillae and premaxillae surrounding the vomer and large 

 mesethmoid (fig. 93, 11), which sends forwards a long partially 



