'1EETH OF LIZARDS. 



275 



PLEURODOXT JAW (iGUANA), FROM WITHIN. 



Common observation instructs us that many Lizards leave their tails behind in the hand of their 

 incautious captor, without seeming any the worse for this singular loss of much of the organ. The 

 vertebrae of the tail are not solid and bony, for there is a space running right across each, in its middle, 

 formed of gristle, or even of cellular tissue, and this gives way nearest the point of greatest stress upon 

 the tail, which snaps off, but will be reproduced. 



Certain skin glands exist, and are seen at the surface along the inner part of the thigh as pores 

 (femoral and inguinal pores), and others exist in front of the vent. They secrete a reddish fatty sub- 

 stance, which often hardens in the duct leading to the 

 pore, and forms a visible projection. 



The teeth of the Saurians are on the pre-maxillse, 

 maxilla?, and the dentary pieces of the lower jaw or 

 mandible, but they often occur also in the pterygoid and 

 palatine bones. 



It was mentioned that the teeth of the English 

 Lizards are pleurodont. This is a term which implies 



that the teeth are attached to a kind of parapet of bone which is placed on the jaws. The teeth are 

 inside this, or between it and the cavity of the mouth, and are attached to it, each tooth by one side, 

 and they are therefore not placed in sockets. 



This arrangement is common to several groups of the order, and others have what is called an 

 acrodont dentition. That is to say, the bases of the teeth are on and are attached to the top of the 

 parapet, and not to its side. The teeth are numerous and simple in structure, and their crowns 

 have very different forms, being sharp, blade-like, or broad, rounded, and crushing, according to the 



outwards to join the commencing backward prolongation of the pterygoid. This is seen in the Snake also, but not in the 



Crocodile ; but the junction, perfect in the Lizard, is movable in the Serpents. In the Lizards the space between the 



prootic bone and the pre-f rental, unlike the 



bony condition of the Crocodile, is filled 



with cartilaginous membrane. There is an 



imperfect bony division between the orbits, 



and the parietal bones form the front part of 



the roof of the brain-case, and the occipital 



the back, hinder, and part of its lower por- 

 tions ; they are not united by sutures or fixed 



in a perfectly motionless manner, but there 



is a membranous interspace, which permits 



of some movement of the face and fore part 



of the skull on the occipital bone. This is SKULL OF CROCODILE. 



very different to the ligid condition of the 



skull of the Crocodile and to the solid structures of that of the snake. On looking at the upper part of the Lizard's skull a 



number of distinct openings are seen. One, the supra-temporal fosM, is bounded by the parietal, post-frontal, and the 



squamosal bones ; and there is a post- and temporal fossa existing between the parietal, the occipital, and a process called the 



parotic. This process is at the back and side of the skull, giving 

 it an angular appearance. It is present also in the Crocodiles, but it 

 is not found in the Snakes. 



A small unossified space, the parietal foramen, usually exists 

 between the parietal bones and the frontals. 



There is also a lateral temporal fossa. The Lizards have the 

 skin over the supra-temporal fossa more or less bony, and it follows 

 that, as in the Crocodile and Chelonians, there is a kind of light 

 outer skull-case, the true brain-case being very small and opening 

 behind at the foramen magnum, where there is, on the basi-occi- 

 pital bone, at its junction with the lateral occipital bones, the solitary 

 condyle for the jointing with the atlas or first vertebra. 



With regard to the lower jaw, the two sides of it are usually 

 united at the chin (or symphysis), and each is composed of six bony 

 pieces. This number is common to the Reptilia, but the junction in 

 front, seen also in the Crocodile, is not observed in the Snake, whose 

 lower jaw is singularly separable from its fellow on its opposite side. 

 Finally, in concluding this notice of the skull, it is necessary to 



mention that the pre-maxillse and maxillpe are firmly united with each other and the skull, and that there are two vomers. 

 Most of the Lacertilia have two small rod-shaped bones, one on each side within the skull. Each extends from a parietal 



bone to the pterygoid nearest to it, and is in close contact with the membranous or cartilaginous wall of the skulL It is 



called the columella, and its presence is of classificatory value. 



SKULL OF RATTLESNAKE. 



