128 ZOOTOMY. 



supplying the heart and stomach, the other becoming the lateral or 

 cutaneous nerve, the distribution of -which has been already seen ( 99). 

 The anterior root of the vagus gives off a small nerve which joins the 

 cutaneus quinti (X c ). 



XXXVII. Lift up the cerebellum and cut it away close 

 to its attachment ; note 



197. The dorsal surface of the medulla oblongata, and 

 the cavity (fourth ventricle, v. 4) inclosed between it and 

 the cerebellum. 



198. The lobi posteriores (/./), a pair of rounded 

 elevations on the anterior part of the floor of the fourth 

 ventricle, and between them a large transverse commissure 

 (cm) passing from one side of the medulla to the other, 

 and in a dorsal view giving the fourth ventricle the appear- 

 ance of two distinct cavities ; that these are continuous may 

 be seen by passing a guarded bristle beneath the commissure. 



XXXVIII. Carefully lift up the posterior edges of the 

 optic lobes and remove enough of them to display 

 thoroughly the cavity thus laid bare : observe 



199. The optic ventricles, large cavities in the optic 

 lobes, continuous with one another in the middle line so 

 as to form in reality a single cavity : the roof of this, just 

 removed, is very thin, its floor extremely thick. 



200. The tori semicirculares (/.j), two somewhat 

 kidney-shaped elevations, situated, one on each side on the 

 floor (crus cerebri) (c.c) of the optic ventricle. 



201. The fornix of Gottsche (/), a somewhat shield- 

 shaped mass, situated between the tori semicirculares, and 

 formed as an infolding of the posterior wall of the optic 

 lobes. 



202. A valve-like plate of nervous matter (x), formed as 

 an infolding of the anterior wall of the optic lobes, and 

 overlapping the anterior end of the fornix of Gottsche. 



