150 



THE NERVOUS SYSTEM. 



a. External form (Fig-s. 98, 102, 103 L.ojj). 



Fig. 103. 



II To Tii.c Hy 



Lateral view of brain of Jlana escuknfa 



Mo 



Ad 

 C 

 Gp 

 lie 



Choroid plexus. 

 Cereb3lluni. 

 Pineal body. 

 Cerebral hemisphere. 

 Pituitary body. 



Tu.c Tuter cinereuni. 

 , ° J > root of olfactory nerve. 



II Optic nerve. 



/ V Trochlear nerve. 

 L,ol Olfactory lobe. V Trigeminal nerve. 



L.ol^ Disc at origin of second root. F// Facial nerve. 

 L.oi) Optic lobe. VllI Auditory nerve. 



Mo Medulla oblongata. /A", A', A'/ Glossopharyngeal, pneumo- 



Tho Thalamencephalon. ga.stric, and accessory nerves. 



To Optic tract. 



The optic lobes 

 are two promi- 

 nent ovoid bodies 

 placed immedi- 

 ately in front of 

 the cerebellum, 

 and connected 

 with it by the 

 valvula cerebelU ; 

 posteriorly they 

 touch each other 

 in the median 

 plane, while an- 

 teriorly they di- 

 verge and thus 

 constitute the 

 widest part of 

 the brain ; in the 

 angle thus formed 



is the thalamencephalon. The optic lobes are always more darkly 

 pigmented than any other part of the central nervous system. 



The Crura cerebri are two columns of white matter, placed beneath 

 the optic lobes, and partly hidden by the pituitary g-land. At their 

 junction with the medulla oblongata, or rather with the pars coiii- 

 mumralis, is a very slight transverse fissure ; at the same point the 

 ventral longitudinal fissure is interrupted by an extremely small 

 grey tubercle (Stieda). 



/3. Internal structure. From the anterior extremity of the 

 foiu-th ventricle a canal, the Sylvian aqueduct (^Aqueduct us S>/lvu, 

 iter a tertio ad quartum ventriculum), may be traced forwards under 

 the cerebellum, in the median line of this section of the brain. At 

 about opposite the middle of the length of the optic lobes the canal 

 is dilated and communicates with the cavities or ventricles [Ventri- 

 culi lobi ojdici, Stieda) enclosed by these ; a general cavity is 

 formed, which in transverse section has something of the form 

 of the letter y. The roof of the cavity is thinner than the floor; 

 this is especially the case in the median plane opposite the superior 

 longitudinal fissure between the optic lobes ; the floor is thinned 

 in the middle line by the descending portion of the cavity. The 

 cavity of each optic lobe extends both forwards and backwards 

 beyond its point of communication with the dilated Sylvian aque- 



