1873.] HULKE — ANATOMY OP HYPSILOPHODON POXII. 525 



lary series, and the larger form occupying a posterior position. In 

 both varieties one surface of the tooth (that towards the cavity of the 

 mouth in the lower jaw, and the outer in the upper jaw) is exquisitely 

 sculptured by longitudinal ridges passing from a raised cingulum 

 at the junction of crown and root to the free border of the crown. 

 The general outline of the crown is subrhomboidal. Both surfaces, 

 longitudinally and transversely, are convex. In a nearly perfect 

 tooth of the smaller variety (fig. 4), which had only just come into 

 use, the cingulum forms an angle open towards the summit of the 

 crown. The principal ridge runs from the open nearly axial angle 

 to the trenchant border, and it forms the apex of the crown. At 

 each side of it is a small secondary ridge ; one of these does not 

 quite reach the cirigulum. Between the free ends of these minor 

 ridges, which give this part of the border of the crown a coarse ser- 

 ration, and the lateral terminations of the cingulum, the sides of the 

 crown are very finely serrated, recalling in miniature the marginal 

 serrature of the teeth of Iguanodon ManteUi. In the larger variety 

 the ornamented surface of the crown is sculptured by a greater 

 number of ridges ; and these are more equal in size (fig; 6). Some of 

 them divide near the trenchant border of the crown, rendering this, 

 when unworn, beautifully crenated; and the sides of these larger teeth 

 are beautifully serrated, as in the smaller variety. The cutting-border 

 of these larger teeth, before it has been worn, is rounder in outline 

 and less angular than that of the smaller ones. The unridged sur- 

 faces of the crowns bear a few very minute inconspicuous striae. All 

 crowns which have risen above the crest of the outer parapet of the 

 jaw bear marks of wear. They are obliquely ground; the sculp- 

 tured surface remains longest, and it forms a cutting-edge, which 

 is at first serrated by the cross sections of the longitudinal ridges, 

 but later becomes merely sinuous as these grow less prominent in 

 the level of the lateral angles of the crown. The maxillary tooth 

 of Mr. Fox's skull, figured in pi. 1. voL xxvi. Quart. Journ. Geol. 

 Soc, is thus worn. The worn surface of large crowns is marked by 

 slight elevations not deserving the name of ridges, running between 

 the inner and outer surface ; and the attritional striae, which are 

 discernible in all worn teeth, have the same direction. By the time 

 that the crown has become worn down to the level of the outer 

 border of the jaw, the long cylindroid fang also has nearly disap- 

 peared, so that very slight force would detach the remnant of a 

 tooth in this condition. The successional teeth rise at the inner side 

 of the old ones, as in existing lizards. 



Attachment of Teeth. — A transverse section through the fang of a 

 cylindric tooth in situ shows it to be contained in a distinct, separate 

 socket. "With respect to the compressed teeth, I am inclined to 

 think that the same does not strictly obtain. As in Iguanodon 

 ManteUi, the outer Avail of the tooth-groove sends inwards partitions, 

 which practically separate the teeth from one another, and must 

 have afforded them a very firm support; but I doubt if these 

 partitions actually reached the inner wall and became confluent 

 with it. 



VOL. XXIX. PART I. 2 N 



