REPTILES. 227 



to shew tliat these proportions afford no measure of the greater or 

 less perfection of organisation. The Ibrain of reptiles presents on the 

 upper surface a great resemblance to that of fishes. The hemi- 

 spheres are still without convolutions, but always hollow inter- 

 nally [lateral ventricles), and surpass in circumference the second 

 portion of the brain, the mass of the corpora quadrigemina 

 or optic lobes, which in the bony fishes constitute the principal 

 mass of the brain. These optic lobes are larger in proportion to 

 the size of the eyes, as in the chameleon; they are hollow inter- 

 nally; between them and the hemispheres, and partially covered 

 by both, are placed the thalami of the optic nerves, which here are 

 still small and, as always, without an internal cavity. In front of 

 the corpora quadrigemina lies the pineal gland, not covered by 

 the ventricles of the brain. The cerebellum is feebly developed in 

 frogs, and consists almost solely of a thin plate of medulla where 

 the two lateral walls of the fourth ventricle approach each other. 

 A laminated part, of a red colour, is attached to its posterior 

 margin, and covers the fourth ventricle of the brain at its upper 

 part\ A similar part is present in tortoises, and has been named 

 by BoJANUS the vascular covering of the fourth ventricle. More- 

 over in these animals, as also in the lizards and especially in the 

 crocodiles, the cerebellum is more fully developed. On the under 

 surface of the brain there is not found, any more than in birds and 

 fishes, the transverse commissure in front of the cerebellum above the 

 medulla oblongata, which in man and mammals forms the bridge of 

 Varolius. In the lizards, especially in the crocodiles and in the 

 serpents, the brain is broader, whilst in the tortoises, as in the frogs, 

 it is narrow and elongate 2. The cerebral nerves correspond, on the 



1 Caeus, op. cit. s. 175 — 179, Tab. in. figs, i — 3. 



2 The brain of Alliyator has been figured by Mueller, Vergl. Neurol, der Myxl- 

 no'iden, Tab. iv. fig. i ; that of the fresh-water tortoise by Bojanus, whose figures 

 have been in part copied in Wagner Icones physiol. Tab. 23 (which may be consulted 

 for the entire comp. anat. of the brain) ; of the brain of Rana, besides Carus, Kuhl 

 also gave figures, as also of Agama marmorata, Lacerta agilis and Coluber natrix, 

 Beitrdge zur vergl. Anatomic, Tab. ITI. s. 57 — 60; the brain of Proteus has been 

 described and figured by Treviranus, Comment. Societ. Goetting., Vol. iv. 1819, pp. 

 197 — 102, Tab. I. II. by EuscoNi Del Proteo angiuno Monografia, Tab. iv. fig. 4, 

 and by Van Deen Tijdschr. voor nat. Gesch. en Physiol, i. bl. X'Z'j, PI. vi, fig. 2; of 

 the brain of the chameleon Treviranus has given a description and figures, Beohach- 

 tungen aus der Zootomie u, Physiol. 1839, s. 93, 94, Tab. Xli. figs. 81, 8-2, &c. 



15—2 



