480 THE VERTEBRATE SKELETON. 



zygomatic arch standing away from it. The temporal fossa is 

 of great size. 



In the PINNIPEDIA the cranial cavity is large and rounded. 

 The skull is much compressed in the interorbital region, and 

 in correlation with this compression the ethmo-turbinals are 

 little developed, while the maxillo-turbinals are large. The 

 orbit is large, and the temporal fossa smaller than in the 

 Carnivora vera. In the Walrus (Trichechus) the anterior part 

 of the face is distorted by the development of the huge canines. 

 The Otariidae have an alisphenoid canal. The tympanic bulla 

 is small in Otaria, large in the Phocidae, and flattened in the 

 Walrus. The hyoid is similar to that in Carnivora vera. 



INSECTIVORA. The skull varies much in the different mem- 

 bers of the order Insectivora, but the following points of 

 agreement are found. The cranial cavity is of small size, and 

 is never much elevated. The facial part of the skull is generally 

 considerably elongated, and the nasals and premaxillae are 

 well developed. The zygomatic arch is usually slender or 

 incomplete, and the coronoid process and angle of the mandible 

 are commonly prominent. 



In some Insectivora, such as Galeopithecus, Tupaia, and 

 Macroscelides, the skull shows a higher type of structure 

 than is met with in most members of the order. In these 

 genera the cranial cavity is comparatively large, and the 

 occipital plane is nearly vertical. The zygomatic arch is fairly 

 strong, and the frontal and jugal give rise to postorbital pro- 

 cesses which nearly or quite (Tupaia) meet. The tympanic 

 bulla is well developed, and produced into a tubular auditory 

 meatus, this being specially well marked in Macroscelides. 



In the other Insectivora the cranial cavity is of smaller 

 comparative size, and the orbit and temporal fossa are com- 

 pletely confluent, often without any trace of a postorbital 

 bar. The occipital plane commonly slopes forwards. In 

 the Hedgehogs (Erinaceidae) and Centetidae the tympanic is 

 very slightly developed, forming a small ring. The zygomatic 



