n6 



THE NERVOUS SYSTEM 



peduncle (and in man by the long olfactory tract). In the sheep's brain there 

 diverge from the olfactory peduncle two well-defined gray bands, the medial 

 and lateral olfactory gyri, which are less evident in man; and furthermore, the 

 lateral olfactory gyrus is obviously continuous with the hippocampal gyrus, 

 forming the pyriform area (Fig. 83). All of these structures are closely asso- 

 ciated in function and belong to the rhmencephalon, or olfactory part of the 

 brain, which, because of the greater importance of the sense of smell in the 

 sheep, is better developed in that animal than in man. A prominent longi- 

 tudinal fissure separates this part of the brain from the rest of the hemisphere. 



Inter-ventricular foramen Body of corpus callosum 



Anterior commissure 

 Septum pellucidum^ 



Rostral lamina 

 Rostrum of corpus callosum. \ 

 Genu of corpus callosum { \ ' 



Body of fornix 



\ Hippocampal com. Roofs of third ventricle or tela choriotdea 



Stria med. /Haben. com. 



Splenium 

 fineal 

 body 



Suprapineal recess 

 ', Superior colliculus 

 ' -Primary fissure 



White center of vermis 



Olfactory bulb 

 Medial olfactory gyrus , 

 Anterior perf. substance'; 

 Lamina terminalis 

 Diagonal band 



>'/ ! / / ! Infundib. \ 

 ' / / ,' Third vent. 

 ! ' Massa intermedia 

 i Optic chiasma 

 Preoptic recess 



\ ' \ \ 'Pons 

 \ \ 'Aqueduct 

 * \Lamina quad. 

 \ 'Posterior com. 

 \ * Hypophysis 

 Mammillary body 



Central canal 

 \ Medulla 



\ Medial aperture of 

 \ \ fourth ventricle 

 \ \Tela chorioidea 

 \ * Fourth ventricle 

 ''Anterior medullary 

 velum 



Fig. 84. Medial sagittal section of the sheep's brain. 



This is known as the rhinal fissure; and all that portion of the cerebral cortex 

 which lies dorsal to it is the new or non-olfactory cortex, the neopattium. In 

 contrast to the older olfactory cortex or archipallium, which includes the pyri- 

 form area, the neopallium is of recent phyletic development. It first forms a 

 prominent part of the brain in mammals and is by far the most highly developed 

 in man. 



Interrelation of the Various Parts of the Brain. An examination of a medial 

 sagittal section of the brain will make clear the relation which the various parts 

 bear to each other (Fig. 84). The medulla oblongata, pans, and cerebellum are 

 seen surrounding the fourth ventricle, and are intimately connected with one 



