Integrative Systems 



147 



TELEN- 



DIEN- 



MYELENCEPHALON 



EPIPHYSIS 

 PARIETAL ORGAN, 

 HABENULAR GANGLION' 

 DORSAL 

 PARAPHYSIS 



MONRO'S FORAMEN 

 HEMISPHERE- 



BASAL GANGLION' 

 ANT. COMMISSURE 

 CHORIOID PLEXUS 



post recess 

 ^infundibulum 

 \ \hypophysis 

 v)ptic thalamus 



LATERAL VENTRICLE, 

 BASAL GANGLION 

 HEMISPHEREy 

 OLFACTORY 



OPTIC THALAMUS 

 .EPIPHYSIS 



/HABENULAR GANG 



-TECTUM OPTICUM 



CEREBELLUM 



4TH VENTRICLE 



ANT. COMMISSURE^ 



'VELUM TRANS 

 PARAPHYSIS 



'POST COMMISSURE 



RHOMBOIDAL FOSSA 



Fig. 138. Diagrams of the vertebrate brain, based upon the brain of a cyclo- 

 stome. (A) The brain in sagittal section, with nerves shown as if projected upon 

 the median plane. (B) The brain viewed from above. (Redrawn from Plate, after 

 Biitschli. Courtesy, Neal and Rand: "Chordate Anatomy," Philadelphia, The 

 Blakiston Company.) 



carries with it a network of fine blood-vessels (Fig. 138). This choroid 

 plexus serves to bring blood into close relation to the lymphlike cere- 

 bral fluid which fills the ventricles. At the junction of the roof of the 

 diencephalon with the telencephalon is a small, thin-walled, non- 

 nervous dorsal outgrowth, the paraphysis (Figs. 137, 138), which 

 seems to be of the nature of a choroid plexus which projects from the 

 wall externally instead of internally. (In a strict sense, the paraphysis 

 should be regarded as within the territory of the telencephalon, but 

 structurally it resembles the closely adjacent products of the dien- 

 cephalic roof.) 



The extraordinary feature of the diencephalon is that it gives rise 

 to some highly specialized organs which physiologically are not parts 

 of the central nervous system, but are exteroceptors. From the walls 

 of the diencephalon, as many as four eyes may develop — one pair 



