THE SKELETON IN MAMMALIA. THE SKULL. 481 



arch of Hedgehogs and Gymnura is very slender, the jugal 

 being but little developed and the squamosal and maxilla 

 meeting one another; in the Centetidae the jugal is absent 

 and the arch is incomplete. 



The Moles (Talpidae) have an elongated, depressed and 

 rounded skull with a very slender zygomatic arch formed by 

 the squamosal and maxilla. The nasals are fused together, 

 and the mesethmoid is ossified very far forwards. In the 

 Shrews (Soricidae) there is no zygomatic arch ; the tympanic 

 is ring-like, and the angle of the mandible is very prominent. 

 The hyoid has a transversely extended basi-hyal, a long 

 anterior cornu with three ossifications, and thyro-hyals which 

 are sometimes fused to the basi-hyal. 



CHIROPTERA. In the frugivorous Flying Foxes (Ptero- 

 pidae) the skull is elongated, and the cranial cavity is large 

 and arched, though considerably contracted in front. There 

 are commonly strong sagittal and supra-orbital crests. The 

 parietals take a great part in the formation of the walls of 

 the cranial cavity, the supra-occipital and f rentals being small. 

 The frontal is drawn out into a long postorbital process, but 

 the zygomatic arch, which is slender, and formed mainly by 

 the squamosal and maxilla, gives rise to only a small post- 

 orbital process, so that the orbit and temporal fossa are con- 

 fluent. There is no alisphenoid canal, and the tym panics are 

 very slightly connected with the rest of the skull. The man- 

 dible has a large coronoid process, a rounded angle, and a trans- 

 versely expanded condyle. 



In Insectivorous Bats the skull is generally shorter and 

 broader than in the Pteropidae. The cranial cavity is large 

 and rounded, and has thin smooth walls. The zygomatic 

 arch is slender, and postorbital processes are not generally 

 well developed. The premaxilla is generally small, sometimes 

 absent. The tympanics are ring-like and are not connected with 

 the surrounding bones. The angle of the mandible is distinct. 

 The hyoid in most respects resembles that of the Insectivora. 



K. 31 



