144 



COMPARATIVE ANATOMY. 



The brain of Anura, and still more that of Gymnophiona, 

 reaches a much higher stage than that of Urodeles, which 

 retains to a greater extent a resemblance to the brain of Fishes. 

 In Rana, moreover, the fore-parts of the hemispheres in the 

 region of the olfactory lobes are fused together in the middle line ; 

 in Urodeles and Protopterus they remain distinct throughout. In 

 Ceratodus the hemispheres are fused together dorsally, and in 

 Ganoids ventrally. 



Olfactory lobes may be largely (Amphibia, Polypterus, 

 Ceratodus), only moderately (Sturgeons), or not at all (Protopterus) 

 developed. 



Reptiles. 



The brain of Reptiles reaches a considerably higher stage of 

 development than that of the forms already described, and this is 



FIG. 119. BRAIN OF BLINBWORM (Anguis fragttis). 

 B, from the ventral side.) 



(A, from the dorsal, 



Vff, cerebral hemispheres, narrowing anteriorly to pass into the olfactory tracts (Tro) 

 and the olfactory lobes (Lol) ; ZH, thalamencephalon; with the hypophysis (H) ; 

 MH, optic lobes, encircled behind by the roots of the optic tracts ( Trop) ; HH, 

 cerebellum ; NH, medulla oblongata ; Frh, fourth ventricle ; R, spinal cord ; 

 /, olfactory nerve ; II, optic nerve, with chiasma (Chi) ; III, oculomotor ; IV, 

 trochlear nerve ; V 1 , first division of the trigeminal, with its special ganglion (G 1 ) ; 

 V 2 , V 3 , second and third divisions of the trigeminal, arising from a common root 

 ( V) and ganglion ( 2 ) ; VI, abducent ; VII, VIII, facial and auditory nerves, 

 arising from a common root ; IX, X, XI, glossopharyngeal, vagus, and spinal 

 accessory ; I Sp, II Sp, first and second spinal nerves ; BK, Varolian bend. 



most pronounced by the individual parts coming to overlie one 

 another to a greater extent, and by the larger development 

 of both the peripheral and basal portions of the hemispheres. 



