404 MR. G. E. DOBSON ON THE [Mar. I, 



It will thus be seen that Erinaceus differs in wanting the third 

 lower incisor, and the first upper and lower, and third lower pre- 

 molars. The first tooth behind the preniaxillary suture is un- 

 doubtedly the representative of the corresponding tooth in Gymnura, 

 which, although provided with two roots, must be regarded as a 

 canine, having not only the position but also the form of that tooth 

 in Carnivora. This tooth in Erinaceus has, as a rule, two roots 

 also ; but occasionally, especially in E. europceus and its varieties, 

 these glow together ; and in a skull in the British Museum (see 

 above, fig. 10) the canine has a single long root which extends up- 

 wards and backwards over the premolars. The second upper pre- 

 molar is the most variable tooth : in most species it has three roots 

 with a triangular crown, having its longest horizontal diameter 

 transverse ; in E. inicropus and E. picftis, on the other hand, it has 

 a single root and a circular crown, is external to the tooth-row, and 

 deciduous in the adult animal. It reaches its highest development. 

 in E. eiiropcEus, its lowest form in E. micropvs, which species is 

 further characterized by the imperfection of the zygomatic arch, 

 owing to the absence of the malar bone. Tlie first and second upper 

 molars have precisely the same pattern of crown as described above 

 (p. 391) in Gymnura; but their peculiar form must be studied in 

 young animals while these teeth are still unworn, as the acutely- 

 pointed cusps quickly disappear as the age of the animal increases: 

 the third molar is much narrower than in Gymnura, and, in common 

 with the others, scarcely varies in shape throughout the species. In 

 the lower jaw the greatest similarity prevails in the shape of the 

 teeth between even the most widely separated s})ecies ; but, excejit 

 in the form of the first and second molars (as in the upper jaw), no 

 resemblance can be traced between them and those of Gymnura. 



The vertebral column is made up of 7 cervical, \a dorsal, 6 lumbar, 

 7 sacro-coccygeal, and 5 or G caudal, succeeded by a variable 

 number of rudimentary vertebrae. It is especially notworthy that, 

 with the exception of the caudal vertebrae, the number of the other 

 divisions corresponds exactly to those of Gymnura. The vertebrae 

 differ, however, in the very short condition of the spinous and trans- 

 verse processes, none of them, except the spinous process of the axis 

 and the inferior lamellae of the transverse process of the sixth cer- 

 vical vertebra, approaching those of Gymnura in size ; and the 

 cervical vertebras have no trace of the hypapophysial spines so pro- 

 minent in that genus. Of the seven sacro-coccygeal vertebrae, the 

 three anterior are firmly ankylosed together, and articulated with 

 the iliac bones, so that one vertebra more enters into the articula- 

 tion, and a much more perfect sacrum is formed, than in Gymnura. 

 The short caudal vertebrae show their fundamental similarity oi' 

 structure with those of Gymnura by the presence of similar but 

 rudimentary chevron bones. As in that genus, there are fifteen 

 pairs of ribs (in E. deserti fourteen only) ; but the thorax is com- 

 paratively much less capacious, these animals seeking protection 

 from their defensive armour, not from speed in making their escape. 

 The sternum is similarly nariow and bilobate in front, but differs in 



