346 



CLASS REPTILIA. 



nature of the cord which connects it with tho epiphysis has been expressly- 

 denied by Leydig, and the fact that pigment may bo found in the 

 dorsal (lens-like) part of the wall as well as in the retinal part of the 

 vesicle is not in favour of its optical nature. 



Moreover the absence of a nerve connecting it with the brain at least 

 in some if not in all cases, is against the optical interpretation, if we may 

 judge from what we know of the degeneration of the paired eye. Neither 

 can the frequent presence of the so-called cornea above the parietal foramen 

 be regarded as a strong support of the view, for no such cornea! area is left 

 in cases of extreme degeneration of the paired eyes. While not attaching 

 any importance to the extreme variability of the organ itself, especially 

 in relation to the " corneal " patch on the skin, the case of Cyclodus is 

 difficult to explain on the median-eye hypothesis. For here there is 

 apparently an ordinary pineal body without any eye-liko structure and 



placed in tho parietal 

 foramen, and over it 

 a " corneal " modifica- 

 tion of the skin. From 

 these and other con- 

 siderations it is clear 

 that the interpretation 

 of the parietal organ as 

 an aborted visual or- 

 gan, though it cannot 

 by any means be dis- 

 missed as a baseless 

 hypothesis, must bo 

 received with more 

 caution t h an has 

 hitherto been accord- 

 ed it. 



FIG. 190. Diagrams showing the relation of the parietal The eyelids have 



organ and pineal body of Lacertilia A, in Cyclodus ; B, in * oon\ u 



Chamaeleon; C, in most Lacertilia ; D, in many Lacertilia alreadv (p.OoO) been 



(Calotes, Seps, Leiodera, etc.). 2 parietal organ ; 3 pineal M j mi 



body ; st cord connecting parietal organ and pineal body ; described. lliere 



1 parietal bone (after Snencer). . , 



is a ring of bony 



plates in the sclerotic and a vascular projection of the 

 choroid (pecten) into the vitreous humour. Lacrymal and 

 harderian glands are present. 



A tympanic cavity is present except in the Amphisbaenidae 

 and communicates by wide openings with the pharynx. The 

 columella auris is a bony rod which passes from the fenestra 

 ovalis to the extracolumellar cartilage. The latter is attached 

 to the tympanic membrane. The hyoid arch is far removed 

 from the skull except in the Geckonidae in which it is attached 

 to the epiotic, close to an attachment of the extracolumellar 

 cartilage to the same bone. In the chameleons in which there 



