SUMMARY OF THE TELENCEPHALON.
The telencephalon, or end-brain, forms the most anterior and largest division of the encephalon and comprises the hemisfihaerium, and the tars °pica hyfiothalami.
A. The hemisphaerium includes : The pallium or the cerebral-mantle, The rhinencephalon or the olfactory brain, The stem of the end-brain.
The two hemispheres, separated from each other by the fissura dinalis cer ebri, are connected by the lamina terminalis, the corpus callosum, the commissura anterior and the fornix transversus.
The pallium exhibits the cerebral lobes and convolutions, separated by the inter vening clefts and furrows. As fissures or total furrows are designated those deeply incising chief furrows, which are early developed and which, in consequence of their deep penetration, push in the wall of the ventricle. To these belong : the fissura cerebri lateralis, the fissura parieto-occipitalis, the fissura calcarina, the fissura collateralis and the fissura hippocampi. At the bottom of the fissura cerebri lateralis lies the fossa cer ebri lateralis, which in a measure corresponds to a ventricular protrusion of the corpus striatum. The fissura parieto-occipitalis corresponds to the bulbus cornu posterioris, the fissura calcarina to the calcar avis, the fissura collateralis to the eminentia collateralis, while the fissura hippocampi is responsible for the production of the hippocampus within the inferior horn.
As sulci or cortical furrows are designated the less deeply penetrating grooves which are confined more to the surface of the hemisphere.
The chief divisions of the cerebral mantle are : the lobus frontalis, the lobus parie talis, the lobus temporalis, the lobus occipitalis and the insula. The latter, however, strictly regarded, does not belong to the cerebral mantle, but to the trunk of the end-brain.
The rhinencephalon falls into the peripheral and cortical regions.
The peripheral region comprises the lobus olfactorius, which in turn is subdivided into the lobus olfactorius anterior and posterior.
The lobus olfactorius anterior includes The bulbus olfactorius, The tractus olfactorius, The tuberculum olfactorium, The area parolfactoria of Broca.
From the tuberculum olfactorium the gyrus olfactorius lateralis extends laterally toward the fossa Sylvii, here forms the angulus gyri olfactorii lateralis, then runs back ward and ends as the gyrus semilunaris and gyrus ambiens at the front border of the gyrus hippocampi. The gyrus olfactorius medialis extends medially from the tuberculum,
its continuation forming on the medial surface of the hemisphere the area parolfactoria of Broca, which, in turn, is prolonged upward into the gyrus cinguli.
The lobus olfactorius posterior claims the substantia perforata anterior and the diag onal band of Broca, which latter passes into the gyrus subcallosus, situated on the medial aspect of the hemisphere behind the area parolfactoria.
The cortical region has as its chief components : The gyrus fornicatus, made up of the gyrus cinguli and the gyrus hippocampi with the connecting isthmus.
The hippocampus or cornu Ammonis, pushed into the inferior horn of the lateral ventricle by the hippocampal fissure.
The gyrus dentatus.
The gyrus uncinatus, the gyrus intralimbicus, the gyms fasciolaris and the rudi mentary callosal convolutions or gyri Andreae Retzii. Concerning the connections of the peripheral and central regions consult pages 145-149.
The stem of the has as its most important part the corpus striatum, which is separated by the capsula intern into the medially situated nucleus caudatus and the laterally placed nucleus lentiformis. The latter is subdivided by the medullary lamina: into the putamen and the globus pallidus. To the stem of the end-brain belong, further, the claustrum, separated from the nucleus lentiformis by the capsula externa, and the nucleus amygdalae, located in the extreme front part of the temporal lobe. All these nuclei are connected with the cortex of the substantia perforata anterior.
Within each hemisphere, the lateral ventricle expands into its three horns, the anterior, posterior and inferior, and the uniting body or pars centralis. The two lateral ventricles communicate with each other and with the third ventricle through the foramen interventriculare or foramen of Monro.
B. The pars optica hypothalami includes : The lamina terminalis, The chiasma opticum, with the tractus optici, The tuber cinereum, The infundibulum, The hypophysis.