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"=). 



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 (t.s), 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 {f.G\ 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 (*•), formed as 

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

 overlapping the anterior end of the fornix of Gottsche. 



