408 CEREBRUM. 



nerve or portio mollis. This cavity is lined in most of its 

 extent by gray neurine. 



CEREBRUM OR UPPER BRAIN. 



The Cerebrum, (Fig. 16,) styled the brain proper, is sit- 

 uated- within the cranial cavity, occupying the whole of 

 this cavity extending from the vault to the tentorium, by 

 which latter it is separated from the lower brain or cere- 

 bellum. 



It is about seven times heavier than the cerebellum, 

 weighing from two and a half to three pounds. The brain 

 of man is heavier than that of any other animal. Its 

 form is oval, and its average diameters are as follow : the 

 antero posterior about six inches, the transverse in its 

 greatest breadth about five, and the vertical between four 

 and five. It is divided into two lateral and symmetrical 

 parts by a deep fissure which runs along the median line, 

 separating the cerebrum in its whole depth, but inter- 

 rupted by the corpus callosum in the middle. This fissure 

 receives the falx major and the anterior and cerebral arte- 

 ries and veins, and the two lateral portions thus divided 

 are called hemispheres. Each hemisphere is again divided 

 into three lobes, an anterior, middle, and posterior lobe. 

 The anterior or frontal lobes are small and are situated 

 upon the orbitar plates of the frontal bone. The middle 

 or temporal are large and prominent, occupy the middle 

 fossa in the base of the cranium, and are separated from 

 the anterior by the deep fissure of Sylvius. This fissure 

 receives the middle cerebral arteries. 



The posterior lobes rest upon the tentorium, having but 

 a slight mark of separation from the middle, which how- 

 ever corresponds to the superior ridge of the petrous bone. 

 The surfaces of the cerebrum are superior, inferior, and 

 lateral. Its general form has just been stated to be oval, 

 but as it exactly corresponds with the cranial cavity, its 

 shape will vary with the shape of this cavity. The form 

 of the superior surface is convex, corresponding to the 

 concave vault of the cranium the inferior is flat ; adapted 



