XIII 



PHYLl'M CHORD ATA 



400 



distinct, yet mark out the surface into lobes or convolutions not 

 distinguishable in the case of the Pigeon or the Lizard, A slight 

 depression — the Sylvian fissure — at the side of the hemisphere 

 separates off a lateral portion, or tcniporal lohe (Fig. lOOG, c.h~.), 

 from the rest. There arc very large club-shaped olfactory bulbs at 

 the anterior extremities of the cerebral hemispheres, and behind 

 each on the ventral surface of the hemisphere is the corresponding 



C.TA 



c.r* 



Fig. lO'.'o.— Lepus cuniculus. Two dissections of the brain from above (iiat. si/^e). In A the 

 left parencei>balon is dissected down to the level of the corpus callosum : on the right the 

 lateral ventricle is exposed. In B the cerebral hemisiiheres are dissected to a little below 

 the level of the anterior genu of the corpus callosum ; only the frontal lobe of the left 

 heniispliere is retained ; of the right a portion of the tcmjioral lolie also is left ; the velum 

 interposituni and pineal body are removed, as well as the gi'eaterpart of the body of the fornix, 

 and the whole of the left posterior pillar ; the eereb;lhim is removed with the exceiition of a 

 part of its right lateral lobe. a. ro. anterior comnnssure ; n.fo. anterior pillar of fornix; 

 (!. p/i. anterior peduncles of cerebellum; b./o. body of fornix; clA. siiptrior %-ermis of cere- 

 V)ellum ; r//-. its lateral lobe; r. pa. corpus gcniciilatum ; <;. k. cerebral hemisphere; rk.pl. 

 choroid plexus ; ry). cl. corpus callosum ; cp. s. corpus striatum ; c. r.?. corpus restifornie ; 

 d. p. dorsal pyramid ; rf. floc(*ulus ; hj>. m. hippocampus ; m. en. middle commissure ; o. l^. 

 anterior, and o. ?'-. posterior lobes of corpora quadrigemina ; o. Ih. optic thalamus ; o. tr. optic 

 tract ; p. co. posterior commissure ; p.fo. posterior pillar of fornix ; pn. pineal body ; pd. pn. 

 peduncle of pineal Ixidy ; /i. pn. posterior peduncles of cerebellum ; yi. va. fibres of pons 

 Varolii forming middle peduncles of cerebellum ; sp. lu. septum lucidum ; si. I. stria longi- 

 tudinalis ; t. .1. taenia semicircularis ; v. vii. valve of Vieussens ; r3, third ventricle ; i;4, fourth 

 ventricle. (From Parker's Zootomy/.) 



olfactory tract leading back to a slight rounded elevation, the 

 tiibcrculum olfactorium. Connecting together the two hemispheres 

 is a commissural structure — the corpus (■allosuni (Figs. 1095, 1096, 

 cj). c/.) — not present in the Pigeon ; this runs transversely above 

 the level of the lateral ventricles. Examined in transverse section, 

 i.e., in a longitudinal section of the brain (Fig. 1096), the corpus 

 callosum is seen to bend sliglitly downwards, forming what is 

 termed the gemc; posteriorly it bends downwards and forwards, 



