THE DIENCEPHALON AND THE OPTIC NERVE 



221 



the sensory nuclei of the trigeminal nerve. If this be true, the mechanism in 

 question may receive afferent impulses from the nose, mouth, and tongue and 

 be concerned with feeding reflexes. 



The pineal body is a small mass, shaped like a fir cone, which rests upon the 

 mesencephalon in the interval between the two thalami. Its base is attached 

 by a short stalk to the habenular and posterior commissures, and into the stalk 

 there extends the small pineal recess of the third ventricle. The pineal body is 

 a rudimentary structure and is not composed of nervous elements. In some 



Hypothalmic sulcus 



Habenula 

 Habenular commissure^ \ 



Suprapineal recess i > 



\ \ \ 



Posterior commissure \ \ \ 



Pineal body \ \ \ 

 Splenium of corpus callosum N \ \ \ *. ' 

 Lamina quadrigemina \ \ \ 



\ N ^/ X v > 



Cerebral aqueduct N N ^ v x s A \ \ \^-^ 



s N v v'-^rr 



Anterior medullary velum, 



Fourth ventricle N 

 5w/>. z;erw. of cerebellum x 



Fissura prima N_J 



Inferior vermis 

 of cerebellum 



Epithelial roof and chori- 

 oid plexus of fourth''' 

 ventricle 



, Body of fornix 



Chorioid plexus of third ventricle 

 Massa intermedia 



Epithelial roof of third ventricle 

 I Lamina commissure hippocampi 

 1 t Corpus collosum 







Genu of corpus 

 ' callosum 



Septum pelluci- 

 J^'^ dum 



^"~~ Ros.ofcor. callosum 

 ~ - Lamina rostralis 

 " Columna fornicis 

 ^-~~^ Interventr icular foramen 

 ^^.^ Anterior commissure 

 *-^~ Lamina terminalis 

 ^-C^Optic recess 

 ^*- ^Optic chiasma 

 ~ -^ Infundibulum 



Hypophysis 

 Mammillary body 

 Oculomotor nerve 

 \ *Subthalamus 



Tegmentum of mesencephalon 

 Pans 

 Medulla 



'Central canal 



Fig. 158. Median sagittal section through the human brain stem. 



vertebrates, certain lizards for example, it is more highly developed, resembles 

 in structure an invertebrate eye, and lies close to the dorsal surface of the head. 

 The posterior commissure is a large bundle of fibers which crosses the median 

 plane dorsal to the point where the cerebral aqueduct opens into the third 

 ventricle (Figs. 154, 156). The source and termination of the fibers which 

 constitute the bundle are still obscure. 



