146 



COMPARATIVE ANATOMY. 



lower organisation than that of other Reptiles. The hemispheres 

 are small and pyritV.rrn, 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). OUaetory lobes seem to be wanting in Crocodiles only. 

 An olfactory ventricle is usually present in each lobe. 



Kn;. 121. liitAix OF ALLIGATOR. (From the dorsal side.) 

 (After Rabl-Riickhard.) 



TIT, cerebral hrniis|ihnvs ; Z, pineal gland ; MTf, optic lobes ; 7/77 and 7777 1 , 

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

 boinnii'd l>v tin- cininriiii;!' acustica: (K</<- . Ilie tsenise mednllares (?'), the obex 

 i .'//,), ami tlir i-lava (67) ; I, olfactory nerve : //, optic nerve ; //', troi.-hlrar nerve; 

 V, trigrniinal, /'///, auditory. IX, glosaopharyngeal, X, vagus, XI, spinal 

 accessory, and 7 >>/, 1 1 Xji, lirst and srruiid spinal nerves. 



The thalamenceghalon is always depressed, and is hardly, 

 or nut (\\ ;dl, \isilile iVum the dorsal side. It gives rise to a 

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

 embryos of l/i/;irds, as in those of Annra, extends into the roof of 

 the skull, but which becomes narrowed and reduced later. 



The mid -bra in always consists of a well-marked paired 

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

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



