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Show 404 MR. G. E. DOBSON ON THE [Mar. 1, It will thus be seen that Erinaceus differs in wanting the third lower incisor, and the first upper and lower, and third lower premolars. The first tooth behind the premaxillary suture is undoubtedly 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 grow together; and in a skull in the British Museum (see above, fig. 10) the canine has a single long root which extends upwards and backwards over the premolars. The second upper premolar is the most variable tooth : in most species it has three roots with a triangular crown, having its longest horizontal diameter transverse ; in E. micropus and E. pictus, 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. europa?us, its lowest form in E. micropus, which species is further characterized by the imperfection of the zygomatic arch, owing to the absence of the malar bone. The 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 species; but, except 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, 15 dorsal, 6 lumbar, 7 sacro-coccygeal, and 5 or 6 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 transverse processes, none of them, except the spinous process of the axis and the inferior lamellae of the transverse process of the sixth cervical vertebra, approaching those of Gymnura in size; and the cervical vertebrae have no trace of the hypapophysial spines so prominent 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 articulation, and a much more perfect sacrum is formed, than in Gymnura. The short caudal vertebrae show their fundamental similarity of 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 comparatively much less capacious, these animals seeking protection from their defensive armour, not from speed in making their escape The sternum is similarly narrow and bilobate in front, but differs in |