NERVOUS SYSTEM AND BRAIN. presents two small rounded eminenees, the in- ternal and the external geniculate bodies. The tania semieireularis is a narrow band of white libres which lies in the depression between the caudate nucleus and the optic thalamus. An- teriorly, it follows the deseenilin;; pillar of the fornix ; posteriorly, it passes into the descending liorn of the ventricle, and at the bottom of the horn enters a mass of gray matter known as tha nucleus amygdahe. The velum interpositum is a vascular extension of the |)ia mater into the interior of the brain through the great transverse fissure. It enters the tliird ventricle beneath the corpus callosum and above the optic thalami, corpora quadrigc- (iim(4) mtm (SM) (S) DIAGRAM OF THE CELL9 Of THE CEREBRAL CORTEX. A. Sii|)ertlcial or nioli'ciilar Irt.vfT; (/) funifi)riii : (i>) tri- aiijurulnr; (.V) pol.VK'Xi'il c«*I1s of ('jiiiil. H. I.ji.vtT nf Hiimll p.vfamldM; {4 Hiiuilli'Ht; (.7) sitiull ; ('»') rinMliuiri.sIzod pyram- idal ct'llH with tht'ir axcmi'S ilfsri'mihiif U^ tho whit^ matter. Klvin^f off coUatiTfilH in tlii-ir course. C, Lnyer of larfft' pyrutnlilal ct^Hs; (") larKo p.vniiiiidnl cflU witii very niiiiH'rou.-^ liendritt'H: v**) larK»'Ht j^iant pyramidal cells; (.*/) Mnrtlnottl coll with dcBcomJin^; dendrites and aHciMidtnj? a.xniie; {10) polygonal ccIIh. It. Iie»'p layer; (77) fusiform ccIIh; (/!') polyKonal ceilH. K. The white matt«r eoiituln- liiK axones from pyranililal cells : {4). (.7). («). (*), and from cella (12) o( the deep layer : (US) neuroglia fibre. mina. and pineal gland. Anteriorly, it bifurcates, a part entering each lateral ventricle through the foramen of Monroe. In the thinl ventricle two vascular fringes hang down from the velum. These are the choroid plexuses of the thirl ventricle. In the lateral ventricles similar fringes are attached to the lateral margin of the velum. These are the choroid plexuses of the lateral ventricles. Tlip corpus (imbriatum or tania hippocampi is the lateral edge of the posterior pillar of the fornix. It is a narrow white hanil lying just behind the choroid plexus of the lateral ventricle. 382 NERVOUS SYSTEM AND BRAIN. The fornix is an arcli-shapod band ot white fibres, running longitudiiuiUy, which bifurcates both anteriorly and |)Osteriorly, forming the an- terior and the posterior pillars of the fornix. The central portion or body of the fornix is tri- angular in shape, its narrow anterior en<l being attached to the septum luoidum, its broad pos- terior extremity being continuois with the cor- pus callosum. The anterior pillars curve down- ward in the lateral walls of the ventricle and enter the corpora albicantia, from which they pass into the optic thalami. The i>osterior pillars of the fornix pass downward in the de- scending horns of the lateral ventricle, their thin margin forming the already described corpora fimbriata. The hippocampus major or cornu Ammonis, so called from its fancied resemblance to a ram's horn, is a long cur'ed body consisting of both gray matter and white matter which follows the curve of the floor of the middle horn of the lateral ventricle. It is formed by an extension inward of the dentate sulcus. The gray substance of the sulcus forms an irregular ridge along the margin of the hippocampus major, known as the fascia dentata. The lower end of the hippo- campus major is marked by several rounded ele- vations which from their resemblance to the paw of an animal are known as the pes hipiiocamjii. The hippocampus minor is a longitudinal emi- nence in the iloor of the posterior horn of the lateral ventricle. It is due to the extension inward of the calcarine sulcus. The emincncia collateralis or pes accessorius is an eminence caused by the inward projection of the collateral fissure, 'it lies between the hipiiocanipus major and hippocampus minor, and between the poste- rior and descending horns of the lateral ventricle. General Histology of the Cereurum. Each cerebral convolution consists of a central white core covered over by a layiT of gray matter, which latter constitutes the cerebral cortex. The cerebral eorte.x may be divided into three fairly distinct layers: (1) an outer barren or mole- cular layer; (2) a middle l.iyer. or layer of pyramidal cells; (3) an inner layer, or layer of polymorphous cells. ( 1) The nerve cells of the barren or molecular layi'r are known as the cells of C'ajal. They are fusiform, triangular, or irregular in shaiic, and both their dendrites and axones ramify in this outer layer, the axones passing mainly in a direction parallel to the surface. This layer also contains the terminations of the apical den- drites of the pyramidal cells, some medullated nerve fibres running parallel to the surface, called superficial tangential fibres, ami a rich jiU'Xus of neuroglia. (2) The layer of pyramiilal cells is often de- .scribed as two separate layers, an outer layer of small i)yraniidal cells, and a deeper layer of large i)yramiilal cells. Each pyramidal cidl has ]>assing olV from its outwardly directed angle a large ajiical or main dendrite. Smaller ilcn- dritcs iiass olT from the sides and base of the cell. The axone originates from the base of the cell and enters the white matter of the corona radiata. During its passage through the gray matter it sends off collateral branches. Some of these collateral branches are nu'dullatcd and form the deep tangential filires. .Among the deeper cells of this layer are foimd some very large pyramidal cells, called the cells of
