CONSIDERATIONS OF THE BRAIN OR ENCEPHALON. 



37 



separated from the middle area by the fossa and fissura lateralis 

 cerebri. The frontal lobe of the cerebral hemisphere, on either 

 side of the longitudinal fissure, makes up nearly all this area. 

 The inferior surface of the frontal lobe is concave and is adapted 

 to the convex orbital plate of the frontal bone; its medial border 

 is most prominent and presents, near the longitudinal fissure, an 

 elongated gray mass, the olfactory bulb (if it has not been torn 



Fig. 18. Diagrammatic sagittal section of vertebrate brain. 

 (Morris's Anatomy after Huxley.} 



a. Corpora quadrigemina. b. Mid-brain, c. Pineal body. d. Cerebellum (hind -brain). 

 e. Medulla oblongata (after-brain), f. Pons Varolii (hind-brain), g. Lateral ventricle. 

 h. Cerebral hemisphere, i. Corpus striatum. j. Olfactory diverticulum. k. Pedunculi 

 cerebri. 1. Thalamus, m. Inter-brain, n. Hypophysis. O. Interventicular foramen. 4. 

 Fourth ventricle. 5. Aqueduct of cerebrum. 3. Third ventricle. 



off) and a white strand, the olfactory tract. Running backward 

 from the bulb, parallel with the longitudinal fissure of the cere- 

 brum to the fossa lateralis cerebri, the olfactory tract is seen to 

 bifurcate into two distinct striae, a medial and a lateral. 



The middle area of the inferior surface of the brain is prom- 

 inent laterally where it is formed by the temporal lobes of 

 the cerebrum. It is depressed in its median portion and thus 

 adapted to the hypophyseal region of the cranial floor. This 

 median hypophyseal region extends from the end of the longit- 

 udinal fissure, in front, backward to a great white, transversely 

 striated eminence, called the pons; it contains several important 

 structures, viz., the bases pedunculi; posterior perforated sub- 

 stance; the mammillary bodies; tuber cinereum and stem of the 

 infundibulum; optic chiasma, tracts and nerves; lamina cinerea 

 terminalis; and the anterior perforated substance. 



Issuing from the under surface of the cerebral hemisphere and 



