200 REPTILIA. 



panied by the appearance of a special gland (Harderian gland) . Peculiar 

 folds of the choroid, which correspond to the processus falciformis 

 of the eyes of Fishes and to the so-called pecten of the eye of Birds, 

 are present in the eye of Lizards. 



The auditory organ has a simple tubular cochlea and a corre- 

 sponding fenestra (fenestra rotunda). A tympanic cavity with 

 Eustachian tube and tympanic membrane is wanting only in the 

 Snakes and apodal Lizards. In these cases the operculum, which 

 covers the fenestra bvalis, and the columella which is attached to the 

 operculum, are buried among the muscles, as in numerous Amphibia. 

 When a tympanic cavity is present, the columella is applied by its 

 cartilaginous end to the tympanic membrane, which in many Lizards 

 is still concealed beneath the skin, while a wide Eustachian tube leads 

 into the pharynx. A cutaneous fold above the tympanic membrane 

 of the Crocodiles may be regarded as the first rudiment of an ex- 

 ternal ear. 



The olfactory organ of the Reptilia shows, principally in the 

 Chelonia and Crocodilia, a considerable augmentation of the surface 

 of the mucous membrane, the folds of which are supported by carti- 

 laginous turbinals. The external nares can be closed only in the 

 Water- Snakes and the Crocodiles by an arrangement of valves. In 

 the Crocodiles and Chelonians the internal nares open far back on 

 the palatal part of the mouth. In the Snakes and Saurians there is 

 / also a second olfactory organ embedded between the turbinals and 

 the vomer (nasal glands, Rathke, Jacobsons organ, Leydig), the 

 nerve of which arises at the end of the olfactory lobe, and is spread 

 out like a cup around a cartilaginous papilla. 



The sense of taste is by no means always located in the tongue, 

 since in Snakes and many Lizards this organ serves for feeling, and 

 in other cases e.g., the Chamseleon is used as a prehensile organ. 

 Leydig* has recently discovered cup-shaped sense-organs in the 

 buccal cavity of Snakes and Saurians. In the Snakes they are 

 arranged alongside the rows of maxillary teeth, in Saurians they are 

 embedded in small pits of the connective tissue. 



Alimentary canal. Excepting in the Chelonia, whose jaws 

 possess a horny cutting investment, which constitutes a kind 

 of beak, the jaws are provided with conical or hooked prehen- 

 sile teeth, which hold fast the prey, but cannot masticate it. As 

 a rule, the teeth are confined to the jaws, and are always arranged 



* Fr. Leydig, " Zur Kenntniss der Sinnesorgane der Schlangen," Arch, fur 

 . Anatomie, Bonn, 1872. 



