ENCEPHALON. 



79 



Fig. 8. 



on the vault or roof of the orbit, a middle or temporal, filling the mid- 

 dle and lateral parts of the base of the cranium, and separated from 

 the former by a considerable depression, called fissure of Sylvius, 

 and a posterior, which rests on the tentorium cerebelli. This part of 

 the cerebrum is divided into two very distinct portions by the medulla 

 oblongata. Anterior to it are the crura cerebri or cerebral peduncles 

 by most anatomists considered to be a continuation of the anterior fas- 

 ciculi which form the spinal marrow and medulla oblongata, and pro- 

 ceeding to form the hemispheres of the brain. Between the anterior 

 extremities of the peduncles are two hemispherical projections, called 

 eminentiae mammillares, which are possessed by man exclusively ; have 

 the shape of a pea; and are formed of white nervous tissue externally, 

 of gray within. Anterior to these again is the infundibulum ; and a 

 little farther forwards, the chiasma of the optic nerves or the part at 

 which these nerves come in contact. 



Laterally, and at the inferior surface of the anterior lobes, is a 

 groove or furrow, running from behind to before, and from without to 

 within, in which the olfactory nerve is lodged. At the extremity of 

 this furrow is a tubercle, which is tri- 

 fling in man, but in certain animals is 

 equal to the rest of the brain in bulk. 

 From this the olfactory nerve has been 

 conceived to arise. It is called the ol- 

 factory tubercle or lobe. 



When we examine the interior of the 

 brain, we find a number of parts to 

 which the anatomist assigns distinct 

 names. Of these the following chiefly 

 concern the physiologist. It has been 

 already remarked, that the corpus cal- 

 losum forms at once the bond of union 

 and of separation between the two 

 hemispheres. It is distinctly perceived, 

 in the form of a long and broad white 

 band, on separating these parts from 

 each other. Beneath the corpus callo- 

 sum is the septum lucidum or median 

 septum, which passes perpendicularly 

 downwards, and separates from each 

 other the two largest cavities of the 

 brain-the lateral _ ventricles. It ^ ^JfgSSSL^iS&^\SSSyf 



formed Of tWO laminae, which leave a netalia. 4,5. Anterior and posterior extre- 



., -, 11* i ,1 J /?.7 nrities of the middle fissure of the cerebrum. 



Cavity between them, Called the fifth 6. Anterior extremity of the corpus callo- 



The fnrnir or inferior lonai- ? um : 7> |* posterior extremity joining the 



J.lie JOrHUC IT lUjer Wr lunyi f orn ix. 8, 8. Point to where the corpus 



Commissure Of Mr. Solly, Whose callosum joins the lateral medullary matter 



. J ' of the cerebrum. 9. Its place of junction 



Omce IS tO Connect the anterior and pOS- anteriorly. 10. Posterior point of union. 



n . -I i 'i 11. Middle portion of the corpora striata 



tenor parts of the same hemisphere, as (lateral ventricle). 12. Tamartriata. 



Fornix, &c., as given by a Transverse 

 Section of the Cerebrum. 



trnnvprA r>nrnrmanrA <\f\ tVinP nf Septum lucidum. 



C 



Fornix. 16. Posterior crura. 1 



13. 

 15. 

 Plexus 



the opposite hemisphere, is placed hori- choroicies. is. Ergot or hippocampus 



* . , nor. 19. Posterior crura of the lateral 



zontally below the last. The band of 



nor. 

 ventricle. 



