840 NEUROLOGY 





mammillare. The column of the fornix is joined by the stria medullaris of the pineal 

 body and by the superficial fibers of the stria terminalis, and is said to receive 

 also fibers from the septum pellucidum. Zuckerkandl describes an olfactory fascic- 

 ulus which becomes detached from the main portion of the column of the fornix, 

 and passes downward in front of the anterior commissure to the base of the brain, 

 where it divides into two bundles, one joining the medial stria of the olfactory 

 tract ; the other joins the subcallosal gyrus, and through it reaches the hippocampal 

 gyrus. 



The crura (cms fornicis; posterior pillars} of the fornix are prolonged backward 

 from the body. They are flattened bands, and at their commencement are inti- 

 mately connected with the under surface of the corpus callosum. Diverging from 

 one another, each curves around the posterior end of the thalamus, and passes 

 downward and forward into the inferior cornu of the lateral ventricle (Fig. 750). 

 Here it lies along the concavity of the hippocampus, on the surface of which some 

 of its fibers are spread out to form the alveus, while the remainder are continued 

 as a narrow white band, the fimbria hippocampi, which is prolonged into the uncus 

 of the hippocampal gyrus. The inner edge of the fimbria overlaps the fascia 

 dentata hippocampi (dentate gyrus} (page 827), from which it is separated by the 

 fimbriodentate fissure ; from its lateral margin, which is thin and ragged, the ventric- 

 ular epithelium is reflected over the choroid plexus as the latter projects into the 

 chorioidal fissure. 



Interventricular Foramen (foramen of Monro). Between the columns of the fornix 

 and the anterior ends of the thalami, an oval aperture is present on either side: 

 this is the interventricular foramen, and through it the lateral ventricles communi- 

 cate with the third ventricle. Behind the epithelial lining of the foramen the choroid 

 plexuses of the lateral ventricles are joined across the middle line. 



The Anterior Commissure (precommissure) is a bundle of white fibers, connecting 

 the two cerebral hemispheres across the middle line, and placed in front of the 

 columns of the fornix. On sagittal section it is oval in shape, its long diameter 

 being vertical and measuring about 5 mm. Its fibers can be traced lateralward 

 and backward on either side beneath the corpus striatum into the substance of 

 the temporal lobe. It serves in this way to connect the two temporal lobes, but 

 it also contains decussating fibers from the olfactory tracts. 



The Septum Pellucidum (septum lucidum) (Fig. 720) is a thin, vertically placed 

 partition consisting of two laminae, separated in the greater part of their extent 

 by a narrow chink or interval, the cavity of the septum pellucidum. It is attached, 

 above, to the under surface of the corpus callosum; below, to the anterior part of 

 the fornix behind, and the reflected portion of the corpus callosum in front. It is 

 triangular in form, broad in front and narrow behind; its inferior angle corre- 

 sponds with the upper part of the anterior commissure. The lateral surface of each 

 lamina is directed toward the body and anterior cornu of the lateral ventricle, 

 and is covered by the ependyma of that cavity. 



The cavity of the septum pellucidum (cavum septi pellucidi; pseudocele; fifth 

 ventricle) is generally regarded as part of the longitudinal cerebral fissure, which 

 has become shut off by the union of the hemispheres in the formation of the corpus 

 callosum above and the fornix below. Each half of the septum therefore forms 

 part of the medial wall of the hemisphere, and consists of a medial layer of gray 

 substance, derived from that of the cortex, and a lateral layer of white substance 

 continuous with that of the cerebral hemispheres. This cavity is not developed 

 from the cavity of the cerebral vesicles, and never communicates with the ventricles 

 of the brain. 



The Choroid Plexus of the Lateral Ventricle (plexus chorioideus ventriculus later- 

 alis; paraplexus) (Fig. 750) is a highly vascular, fringe-like process of pia mater, 

 which projects into the ventricular cavity. The plexus, however, is everywhere 



