THE HEDGEHOG OR URCHIN 53 



subepidermic tissue, but is poorly supplied with blood-vessels and 

 without sebaceous and sweat glands. The thickness is no doubt a 

 means of protection, and prevents loss of heat by radiation during 

 hibernation. The skin of the ventral surface is, on the other hand, 

 highly vascular and resembles that of other mammals. Much fat may 

 accumulate on the back, especially in autumn. 



In the skull the palate bones have two large unossified spaces, 

 situated in front of a transverse ridge just behind the posterior molars ; 

 the pterygoid fossae are very broad ; there is no alisphenoid canal ; the 

 mesopterygoid is deep and leads posteriorly into a deep hemispherical 

 excavation lying between the auditory bullae. The sagittal crest may 

 be well developed in specimens so young that the permanent dentition 

 is only just appearing. 



The shape and extent of the premaxillary frontal processes are subject 

 to much variation. In many specimens they are conspicuous, extend- 

 ing backwards for more than half the length of the nasals and with 

 their posterior terminations not sharp or pointed, but blunt or square. 

 This character was at one time supposed to be constant and of sub- 

 specific value in British specimens, and upon it was based the description 

 of ^. europceus occidentalis. Examination of a larger series shows that 

 this is not always the case (see Lonnberg, Ann. and Mag. Nat. Hist., 

 June 1900, 542), but the question cannot yet be regarded as decided. 



Some of the teeth are quite variable in size, especially the second 

 upper incisor and central upper premolar, the former a point of importance 

 because the lesser dimensions of this tooth were fixed upon by de 

 Winton {Proc. Zool. Soc. (London), 1897, 955-956) as diagnostic of 

 E. algirus. Although usually far larger in E. enropmis, this tooth may 

 be occasionally quite small. The central upper premolar is sometimes 

 absent or crowded out of the tooth-line. As regards roots, Hollis 

 (^Zoologist, 1910, 325-6), examining eleven specimens, found the third 

 upper incisor invariably single, the upper canine six times double, once 

 single, and four times intermediate, i.e., single but with indications of 

 fusion of two roots. 



In the upper jaw the central incisors are long and robust, separated 

 and distant throughout their length, their points slightly converging ; 

 the second and third pair, particularly the second, are small and conical, 

 resembling premolars. There is a space between the third and the 

 canine, both of which are usually stated to have single roots, but are 

 very variable in this respect. Of the three premolars, the first two are 

 smaller than the third, which has three roots, and an anterior outer 

 cusp so very large as to resemble the carnassial tooth of a carnivore. 

 The first two molars are large, nearly quadrate, and furnished with 

 strong acute tubercles ; the first molar is the largest of all the upper teeth, 

 the third. is small, placed obliquely, and has to some extent a cutting edge. 



