PHYLUM CHORDATA 



469 



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 temporal lobe (Fig. 1096, c.h^,\ 

 from the rest. There are 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 correspouding 



Fig. 1095.— Lepus cuniculus. Two dissections of the brain from above (nat. size). In A the 

 left parencephalon is dissected down to the level of the corpus callosum ; on the right the 

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

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

 hemisphere is retained ; of the right a portion of the temporal lobe also is left ; the velum 

 interpoaitum and pineal body are removed, as well as the greater part of the body of the fornix, 

 and the whole of the left posterior pillar ; the cereb:llum is removed with the exception of a 

 part of its right lateral lobe. a.co. anterior commissure; a.fo. auterioi" pillar of fornix; 

 a. ?)«. anterior peduncles of cerebellum; b.fo. body of fornix; c&i. superior vermis of cere- 

 bellum; C&2. its lateral lobe; c.fjn. corpus gcniculatum ; c. h. cerebral hemisphere; ch.pl. 

 choroid plexus ; cp. cl. corpus callosum ; cp. s. corpus striatum ; c. rs. corpus restiforme ; 

 d. p. dorsal pyramid ; ft. flocculus ; hp. m. hippocampus ; vi. co. middle commissure ; o. l'^. 

 anterior, and o. l'^. posterior lobes of corpora quadrigemina ; o. th. optic thalamus ; o. tr. optic 

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

 peduncle of pineal body ; p. pn. posterior pedanclcs of cerebchum ; 'p- ^o-- fibres of pons 

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

 tudiualia ; t. n. taenia semicircular is ; v. vn. valve of Vieussens ; cS, third ventricle ; ?;4, fourth 

 ventricle. (From Parker's Zootomy.) 



olfactory tract leading back to a slight rounded elevation, the 

 tuherctdum olfactormm. Connecting together the two hemispheres 

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

 cp, cl.) — riot 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 slightly downwards, forming what is 

 termed the genu\ posteriorly it bends downwards and forwards. 



