REPTILES. 231 



the anterior and posterior apertures of the nasal cavity is very 

 short in the batrachians, very long, on the other hand, in the croco- 

 diles, in which the anterior opening is surrounded by the inter- 

 maxillary bones alone, and is placed on the upper part of the 

 jaw close to its apex; the posterior, a heart-shaped opening at 

 the posterior margin of the palate, is circumscribed by the ptery- 

 goid bones. In the chelonians this cavity is wide and short, and 

 has at the fore part of the bony head an almost quadrangular open- 

 ing, which is bounded by the lateral ethmoid or anterior frontal 

 bones and by the intermaxillary bones. The reptiles never have 

 frontal sinuses comparable to those of mammals. Some cartilaginous 

 folds, continuations of the cartilaginous partition of the nasal 

 cavities, take the place of the superior and inferior turbinated 

 bones, and are covered with a highly vascular mucous membrane 

 provided with black pigment. A cribriform lamella is absent here, 

 as it is in fishes. The olfactory nerve, which is very large, proceeds 

 to the nasal cavity of its side, divides there into branches, and 

 is distributed to the folds of the mucous membrane. In some 

 reptiles there are cartilaginous parts and layers of muscular tissue 

 near the nostrils, by means of which these apertures can be dilated 

 and contracted 1 . 



All the reptiles have two eyes. In most, especially in serpents, 

 they are small in comparison with the size of the body; in the frog, 

 however, in the geckos and the chameleon, they are large. In 

 some they are covered by the skin; in Proteus, the skin is only 

 slightly attenuated, and the stimulus of light appears, according 

 to the experiments of RUDOLPHI, to produce little effect upon this 

 animal. In the serpents and in the genus Gecko also there are no 

 eyelids, but the skin, becoming thinner and transparent, passes over 

 the anterior surface of the eye-ball and forms with the conjunctiva, 

 immediately surrounding the eye-ball, a capsule which is moistened 

 by the lachrymal fluid 8 . In the remaining reptiles there are three 

 eyelids present, of which one is situated perpendicularly at the inner 



1 See on the olfactory organ of reptiles, A. SCAEPA Anatomicce disquisitiones de 

 Auditu et Olfactu, pp. 75, 76; compare also DE BLAINVILLE Principes d'Anat. camp. 

 I. pp. 3*4 330. 



3 On the lachrymal glands of serpents see J. CLOQUET in Mem. du, Mus. d'Hist. not. 

 vn. 1832, pp. 6284, PL n. 



