450 ANATOMICAL TBCBNOLOGY. 



§ 1139. Examination of the Encephalic Segments. — Instru- 

 ments and Materials. — A hemienceplialon, well hardened ; the 

 condition of its lateral aspect may be disregarded. Large and 

 Charriere scalpels, both very sharp. Syringotome or tracer. Fine 

 scissors. Blowpipe. Coarse and fine forceps. Beaded bristles. 

 Small dish or wide-mouthed vial of alcohol, into which the brain 

 and the scalpels may be dipped. 



In dissection of the brain, the scalpels should be very sharp, 

 and dipped in alcohol just before each incision. 



BMnencephalon (examined first on account of its liability to 

 injury during the study of the other parts). — Ventriduct the Lobus 

 olf actorius so as to expose the dorsal aspect of the Cms ol. ; also 

 the Fissura ol. (PI. Ill, Fig. 5, F. ol.) on the ventro-cephalic sxir- 

 face of the hemisphere in which rests the dorsal border of the eras. 



At the junction of the crus with the lobus, note the slight promi- 

 nence of the softer ectal layer, the pero, from which directly arise 

 the olfactory nerves (PI. II, Fig. 3, NN'. ol). Remove the pero 

 with the forceps and tracer, and note that there remains a thin 

 smooth lamina, the pes ol., which is partly fibrous and forms the 

 immediate continuation of the crus. 



The rhinocoelia wUl be more easily seen upon the dissection of 

 another specimen. 



§ 1140. Metencephalon. — Of this segment, one part, the pyra- 

 mis, has been noted. Laterad of the cephalic part of the pyramis 

 is a quadrangular area, the trapezium (PI. II, Fig. 3, tz) ; laterad 

 of its caudal and longer portion are two elevations, here caUed from 

 their outlines. Area elliptica and Area ovalis. 



The dorsal aspect of the metencephalon is overhung by the cere- 

 bellum. Tilt the latter cautiously latero-cephalad, using the tracer 

 to disengage from its ventral aspect the delicate metatela, the roof 

 of the metacoelia (PL III, Fig. 12, mttl). Even if, in so doing, the 

 metatela is torn from its connection with the border of the metacoelia 

 (so as to produce a " Foramen of Magendie," § 1082), it may usu- 

 ally be traced continuous with the ventral surface of the cerebellum 

 just caudad of the epicoelia. 



Now tilt the cerebellum meso-cephalad and note the mass of 

 membrane and blood-vessels forming the metaplexus latereilis 

 (PI. II, Fig. 4; PI. Ill, Fig. 12, mtpx.). 



Upon removal of the metatela and metaplexus, there will be 



