1890.] HEI.ODERMA SUSPECTUM. 205 



tongue in many other reptiles, or with such a lizard, as Varanus for 

 instance, where the morphology of the structure is essentially very 

 different \ 



The Teeth. — These appear to be embedded in the thick buccal 

 membrane that overlies both jaws within the oral cavity in the lizard 

 before us, and it is only in the dried skull that we are enabled to 

 satisfactorily study them. In either jaw the curved line of teeth 

 stand in a slit-like groove of the mucous membrane to which we 

 refer, which is continuous all the way round, and, in addition to this, 

 we find the teeth piercing the basic part of this groove and raising a 

 kind of a papilla at the point of each individual puncture. 



Bocourt has given us excellent figures of the sharp, curved, conical 

 pleurodont teeth of Helnderma (34), and these have been copied by 

 other naturalists ; so it will be quite unnecessary for me to reproduce 

 these now well-known structures here. 



In a very fine mounted skeleton of a specimen of Heloderma 

 suspectum in the collections of the Smithsonian Institution at Wash- 

 ington, which I have been permitted to study, I find the following 

 to be some of the characters of the teeth of this reptile. From 

 twelve to fourteen of these seem to be about the normal complement 

 that are destined to ornament the mandible, while perhaps 

 a pair more are to be found in the upper jaw. In front these 

 teeth are tiny and small ; they very considerably increase in 

 size laterally, while posteriorly they are again smaller, especially in 

 the upper jaw. The largest of all are to be found in the middle of 

 the series in the mandible, the smallest in the premaxilla. Contrary 

 to what I have always understood from published descriptions, I find 

 all of the larger teeth, in both jaws, characterized by the peculiar 

 grooving, although it is best marked in the large ones opposite the 

 site of the poison-gland upon either side. Pleurodont to a less 

 distinctive degree than we find in some other Lizards, these poison- 

 fangs are firmly anchored through anchylosis by a broad base to 

 the rather transversely-spreading ramus, in the case of the mandible, 

 while in the case of the maxilla of the skull they are more laterally 

 attached. When, through accident or otherwise, any of these teeth 

 happen to be lost they are quite rapidly reproduced again, as I 

 have seen from my own observation. 



All curve more or less backwards, and Giinther has said of them 

 that " In the genus Heloderma the teeth are vertically grooved so 

 as to remind us of their structure in Serpents. The teeth indeed 

 are more grooved than in them, for one vertical groove passes down 

 on the antero-inner side and another on the postero-outer side of 

 each tooth" ('Encycl. Brit.' 9th ed. p. 457). 



^ For a good figure of the tongue, hyoiclean arches, and associated parts of a 

 Varanus, see Gegenbaur's ' Elements of Comparative Anatomy' (English trans- 

 lation), p. 553, fig. 310 (Lond. 1878). Ifc is very evident that a biQd tongue, as 

 in the case of a shore humerus in a Swift and a Humming-bird, is by no means 

 an index that all of the remainder of the structure in the compared forms will 

 be more or less alike, and consequently point to affinities that in reality do 

 nob exist. 



Proc. Zool. Soc— 1890, No. XV. 15 



[59] 



