

THE FORE-BRAIN OR PROSENCEPHALON 



813 



of nerve fibers and contains numerous medium-sized nerve cells, the connections 

 of which are as yet not fully determined. 



The corpora mammillaria (corpus albicantia) are two round white masses, each 

 about the size of a small pea, placed side by side below the gray substance of the 

 floor of the third ventricle in front of the posterior perforated substance. They 

 consist of white substance externally and of gray substance internally, the cells of 

 the latter forming two nuclei, a medial of smaller and a lateral of larger cells. The 

 white substance is mainly formed by the fibers of the columns of the fornix, which 

 descend to the base of the brain and end partly in the corpora mammillaria. From 

 the cells of the gray substance of each mammillary body two fasciculi arise : one, 

 the thalamomammillary fasciculus (bundle of Vicq d'Azyr), passes upward into the 

 anterior nucleus of the thalamus; the other is directed downward into the tegmen- 

 tum. Afferent fibers are believed to reach the corpus mammillare from the medial 



miscus and from the tegmentum. 



Tela chorioidea of third ventricle 



Intermediate mags 

 Interventricular foramen 



Posterior commissure 



Corpora quadrigemina 

 Pineal body 



Splenium 



Pia mater 



Genv. 



Rostrum 



Anterior commissure 

 Lamina terminalis 

 Optic recess 

 Optic chiasma 

 Infundibulum 

 Corpus mamillare 



Oculomotor nerve 

 Cerebral aqueduct 



Choroid plexus 



Fourth ventricle 

 FIG. 720. Median sagittal section of brain. The relations of the pia mater are indicated by the red color. 



The tuber cinereum is a hollow eminence of gray substance situated between 

 the corpora mammillaria behind, and the optic chiasma in front. Laterally it is 

 continuous with the anterior perforated substances and anteriorly with a thin 

 lamina, the lamina terminalis. From the under surface of the tuber cinereum a 

 hollow conical process, the infundibulum, projects downward and forward and is 

 attached to the posterior lobe of the hypophysis. 



In the lateral part of the tuber cinereum is a nucleus of nerve cells, the basal optic nucleus 

 of Meynert, while close to the cavity of the third ventricle are three additional nuclei. Between 

 the tuber cinereum and the corpora mammillaria a small elevation, with a corresponding de- 

 pression in the third ventricle, is sometimes seen. Retzius has named it the eminentia saccularis, 

 and regards it as a representative of the saccus vasculosus found in this situation in some of 

 the lower vertebrates. 



