78 



NERVOUS SYSTEM. 



lubricate the brain. This 

 membrane enters into all the 

 cavities of the organ, and 

 in them fulfils a like func- 

 tion. When the fluid accu- 

 mulates to a great extent, 

 the resulting disease is hy- 

 drocephalus chronicus. 



Anatomists usually de- 

 scribe a third tunic of the 

 brain the pia mater. This 

 is generally conceived to 

 consist of the minute termi- 

 nations of the cerebral arte- 



faceof the cerebellum, showing the irbi vitae. 3. Medulla rieS, &nd those of the COr- 



oblongata. 4. Corpus callosum, continuous with 5, the for- rp<?r>rm diner vpin fro-minr* 



nix. 6. One of the crura of the fornix descending to 7, one ^Spending VCinS , lOrmmg 



of the corpora albicantia. 8. Septum lucidum. 9. Velum at the SUrfaC6 of the brain 

 interpositum, communicating with the pia mater of the , , . . 



convolutions through the fissure of Bichat. 10. Section of a VaSCUlar network, which 

 the middle commissure in the third ventricle. 11. Section A -v i 



of the anterior commissure. 12. Section of the posterior paSSCS into the CaVltlCSJ and, 



commissure; the commissure is somewhat above and to the i n flip vpnfriplpa fnrmc +Ko 



left of the number. The interspace between 10 and 11 is the 1LL Ult CB > I( 



foramen commune anterius, in which the crus of the fornix pleXUS chorOldeS and t eld 



(6) is situate. The interspace between 10 and 12 is the fora- * 7 . 7 mi -, 



Longitudinal Section of the Brain on the Mesial Line. 

 1. Inner surface of the left hemisphere. 2. Divided sur- 



men commune posterius. 13. Corpora quadrigemina, upon 

 which is the pineal gland, 14. 15. Iter a tertio ad quartum 



7 .7 m-i , 



CtlOTOlCteCl. Ine ClUra and 

 ertio ad quartum ' y^,,^,. W O,Y. O en Bailor! Kir 

 17. Pons Varolii, P ia ^later Were SO Called by 



UGCU ^JtO-liU, At. J.C*. J.LC 



ventriculum. 16. Fourth ventricle. 



through which are passing the diverging fibres of the corpora the older anatomists, 



pyramidalia. 18. Crus cerebri of the left side, with the . ' 



third nerve arising from it. 19. Tuber cinereum, from which they Were COnCClVCd to be 



projects the infundibulum having the pituitary gland ap- ,1 c -11 ,, > 



pended to its extremity. 20. One of the optic nerves. 21. the Origin 01 all the Other 



membranes of the body. 



7 The cerebrum or brain 



proper has the form of an 

 oval, larger behind. On its 

 outer surface are various un- 

 dulating eminences, called 

 convolutions, because they 

 have been thought to re- 

 semble the folds of the in- 

 _ testines. They are separated 



The Convolutions of one Side of the Cerebrum, as seen fr0m each other by depres- 

 sions called anfractuosities. 

 They form the hemispherical 

 ganglion of Mr. Solly. In 

 the brain of man, these convolutions are larger than in animals; and 

 the anfractuosities deeper. In different brains, the number, size, and 

 arrangement of these vary. They are not the same, indeed, in the 

 same individual; those of the right hemisphere being disposed differently 

 from those of the left. 



The hemispheres, it has been seen, are separated above by the falx 

 cerebri: below, they are united by a white medullary commissure, cor- 

 pus callosum, mesolobe or great commissure, great transverse commis- 

 sure of Mr. Solly. If we examine the brain at its base, we find that 

 each hemisphere is divided into three lobes, an anterior, which rests 



from above. 



1. Anterior lobe of the cerebrum. 2. Posterior lobe. 

 3. Middle lobe. 



