146 



COMPARATIVE ANATOMY. 



lower organisation than that of other Reptiles. The hemispheres 

 are small and pyriform, and all the different parts are narrower 

 and more extended longitudinally ; the brain thus bears a closer 

 resemblance to that of Urodeles (compare Figs. 119, 120, A and B, 

 and 121). 'Olfactory lobes seem to be wanting in Crocodiles only. 

 An olfactory ventricle is usually present in each lobe. 



FIG. 121. BRAIN OF ALLIGATOR. (From the dorsal side. ) 

 (After Rabl-Btickhard.) 



VH, cerebral hemispheres ; Z, pineal gland ; MH, optic lobes ; HH and 



median and lateral portions of the cerebellum ; Frh, sinus rhomboidalis, 

 bounded by the eminentiae acusticse (Eac), the tseniae medullares (T\ the obex 

 (Ob), and the clava (Cl) ; /, olfactory nerve ; //, optic nerve ; IV, trochlear nerve; 

 V, trigeminal, VIII, auditory, IX, glossopharyngeal, X, vagus, XI, spinal 

 accessory, and I Sp, II Sp, first and second spinal nerves. 



The thalamencephalon is always depressed, and is hardly, 

 or not at all, visible from the dorsal side. It gives rise to a 

 distinct infundibulum as well as to an epiphysis, which in the 

 embryos of Lizards, as in those of Anura, extends into the roof of 

 the skull, but which becomes narrowed and reduced later. 



The mid-brain always consists of a well-marked paired 

 portion, and from it the optic tracts pass downwards and forwards 

 to the chiasma. the fibres of the optic nerve taking on a secondary 



