152 THE SKULL. [chap. 



continuous, and there is often not even a trace of a post- 

 orbital process to the frontal or malar. 



In the Erijiaceidoi (Hedgehogs) and the Centetidce the 

 tympanic is a mere ring unankylosed to the surrounding 

 bones, but a kind of bulla is formed by a lamella projecting 

 from the basisphenoid to join its inner and inferior edge. 



In Erinaceiis and Gyinnuni the zygomatic arch is com- 

 plete, but slender, and formed chiefly by the processes of the 

 maxilla and squamosal, which meet each other : the malar 

 being a small splint-like bone attached to the outer and 

 under side of the middle of the arch. In the Centetidcz the 

 malar is entirely absent, and, as the zygomatic processes of 

 both maxilla and squamosal are very short, there is no bony 

 arch. Ce?iteies (the Tenrec) has a remarkably elongated 

 and narrow skull (both cranium and face partaking of the 

 same character), with very prominent occipital and sagittal 

 crests. Both in this genus and in Erinaceiis (the Hedge- 

 hog) the mesopterygoid fossa at the base of the skull is 

 very deep, and ends posteriorly in a hemispherical depression 

 in the basisphenoid, between the wing-like processes which 

 abut against the inner wall of the tympanic. Both parocci- 

 pital and mastoid processes are also well developed. 



The Moles {Talpidc^) have an elongated and depressed 

 cranium, broad posteriorly, and gradually narrowing to the 

 muzzle. The occiput slopes upwards and forwards, the 

 supraoccipital being greatly developed. The zygomatic 

 arches are complete, but very slender, and show no dis- 

 tinct malar bones. There are no postorbital or paroccipital 

 processes. A lamelliform expansion of the upper edge of 

 the periotic {pte7'otic, Parker) forms part of the lateral wall of 

 the cranium, as in the Echidna. The tympanic is united 

 with the other bones of the cranium to form a flattened 

 bulla, produced into a short meatus with a small external 



