680 



THE NERVOUS SYSTEM 



finally disappearing under cover of the temporal lobes. A thin grey lamina, the lamina cinerea, 

 passes from the anterior border of the optic commissure to the commencement of the great 

 longitudinal fissure, where it gains an attacliment to tlie rostrum of the corpus callosum. Tlie 

 crura cerebri ai)j)ear as two strong flattened bundles of white fibres, which emerge from the 

 superior border of the pons, and, diverging from one another, pass under cover of the temporal 

 lobes, and are soon lost to view. On each side the third nerve is seen passing between the 

 posterior cerebral aud superior cerebellar arteries, it springs by a row of filaments from a 

 groove at the inner margin of the crus. The fourth nerve, a slender rounded fasciculus, winds 

 round the outer side of the cnas. The i)ons Varolii aj>})ears immediately behind the crura as a 

 broad band of white fibres directed transversely, and passing from one cerebellar hemisphere to 

 the other. It narrows on each side as it passes into the cerebellum. It is marked by a shallow 

 groove in the middle line in which the basilar artery rests. The fifth nerve is seen jiiercing the 

 side of the pons near its upper border in the form of two bundles, a large posterior or sensory 

 root, and a small anterior or motor root, separated from the former bj' some of the transverse 



Fig. 408. — View of the Ba.se of the Brain. (After Beaunis.) 



OPERCULUM 



3rd or OCULO- 

 ilOTOR 

 ilh nr TRO- 

 CHLEAR 



eth or ABDUCENT- 



Tth or FACIAL 



Sth or AUDITORY. 



»th. GLOSSO- 



PHARTXG. 



lOth. PNEUMO- 



GAST. 



nth. SPINAL 



ACCESS, 

 nth. HYPO- 

 GLOSSAL 



ANTERIOR 



PERFORA TED 



SPACE 

 PITUITARY 



BODY 

 TUBER 



CINEREU.V 

 CORPUS 



ALBICANS 

 POST. PERF. 



SPACE 

 CRUS CEREBRI 

 PONS VAROLII 



OLIVARY BOl'Y 

 AMYGDALA 



INFERIOR 

 VER.MIFORM 

 PROCESS 



fibres of the pons. The sixth nerves are seen at the lower Ijorder of the pons in the groove 

 between it and the medulla, emerging from the latter close to the outer side of the pyramidal 

 bodies or between the fibres of these bodies. The jiyramidal and olivary bodies can readily be 

 made out on the medulla, and a portion of the restiform body can also be seen without disturbing 

 the parts. The twelfth or hypoglossal nerve emerges by a row t)f filaments i'rom the groove 

 between the olivary and pyramidal bodies. The ninth, tenth, and eleventh nerves, which ai)))ear 

 in numerical order from above downwards, arise from the groove })etween the olivaiy and resti- 

 form bodies ; the origin of the eleventh or s]iinal accessory nerve being continued down the lateral 

 column of the ciml. Tlie seventh and eighth nerves are close to the edge ol" the pons in the 

 angle between the latter and the cerebellum. The cerebellar hemis])heres are jjliiced one on each 

 side of the medulla and conceal the occipital lobes of the cerebrum when viewed from the base. 

 The cerebellum stands out C(jnspicuouslv from the cerebi'iun on accoiuit of its darker grey colour 

 and the smaller size and narrowness of its convolutions, which are termed folia. Two of its lobes 

 are more prominent than the rest, viz. the amygdalae or tonsils, which are jtlaced close to the 

 medulla, one on each side ; and the flocculi, which lie close to the pons above the tenth or 

 l)neumogastric nerves. 



