198 REPORT OF NATIONAL MUSEUM, 1898. 



dable as a liorny weapou. Ou the posterior part of tlie inferior face of 

 the thigh in many genera the scales of one or rarely two rows are 

 deeply fossate, and tlie fossae are occupied by a waxy plug, which i)ro- 

 jects beyond the general level. The use of this substance is uncertain, 

 but it is probably an important aid to the animal in maintaining its 

 hold on smooth surfaces. Lizards which move on the ground rest 

 much on the thighs, which are not elevated above the ground in many 

 types, but serve as the principal point of contact from which they make 

 their leaps. The same is true of some genera which leap among trees 

 from branches and trunks. A similar secretion issues from the i)reanal 

 scales in some Iguanidie {Liolaemus, etc.), and in an African Lacertid 

 a rudimental structure of this character is found ou many of the abdom- 

 inal scales (Poroidogaster). An approximation to this structure I have 

 seen on the preanal scales of an adult male of Sceloporus horridus of 

 Mexico. Here the epidermis is greatly thickened above the middle 

 posterior part of the scale, so much so as to make a deep impression 

 in the true skin, simulating a true preanal "pore." I suspect that 

 the nature of these structures is similar to that of corns in higher 

 Vertebrata. 



When the tails of lizards are fractured a cartilaginous rod is devel 

 oped from the centrum of the last vertebra remaining, on which muscles 

 and integument appear. The scales are not similar to those of the 

 normal tail, but resemble generally those of snakes, having a rhombic 

 shape. Sometimes, as in various Scincida3 and Geckonidte, a series of 

 transverse plates is developed on the under side, which does not exist in 

 the normal tail. According to Boulenger the new scales in Lacertidte, 

 Gerrhosauridie, and scinc-like Anguidse reproduce scales of the normal 

 type. This author shows that in the Teiid genus Gynmophthalmus, 

 which has scincoid scales, the reproduced scales of the new tail resem- 

 ble those of the chalcidiform Teiida3, which are totally different. In 

 Bopasia, which has Gerrhonotid scales, those of the reproduced tail are 

 scincoid.^ 



Lizards which live in sandy deserts sometimes have the lateral scales 

 of the digits produced into spines. These probably aid in securing a 

 good foothold in the unstable surface. Such a structure appears in the 

 Geckonid genus Ftenojnis, of South Africa, in the Agamid genus Phryno- 

 cephahis, in Asia, and in the Iguanid genus Uma, in IsTorth America. 

 This is an interesting example of homoplassy.^ 



7. NERVOUS SYSTEM. 



The brain of Sauria may be distinguished as to external form from 

 that of the Ophidia by the less posterior expansion of the i)roseuceph- 

 alon, the hemispheres having about the same width jiosteriorly as the 

 mesencephalon. In the Ophidia the hemispheres spread laterally 

 behind so as to be wider than the mesencephalon. The rhinencephalon 



' Bouleuger, Proceedings, Zoological Society of London, 1888, p. 351. 

 2 Cope, American Naturalist, XXVIII, 1891, p. 435. 



