9O THE GROWTH OF THE BRAIN. 



the bulb. Its cephalic boundary is taken at its junction 

 with those great bundles of transverse fibres which form 

 the pons. This region of the pons has in turn its 

 anterior boundary indicated by a plane passing through 

 its cephalic edge and separating it from the corpora 

 quadrigemina. Between this boundary and a plane 

 passing through the cephalic edge of the corpora quadri- 

 gemina is cut off the fraction of the encephalon known 

 as the mid brain, but it is only rarely that this portion is 

 weighed alone, being usually left in connection with the 

 hemispheres. The hind brain, or cerebellum, is con- 

 nected on each side with the bulb, pons, and the region 

 of the corpora quadrigemina. When all these connec- 

 tions are cut, the cerebellum is separated, and may be 

 weighed either in toto or after further division. The 

 term cerebrum is variously applied to that portion of the 

 encephalon which lies in front of either the cephalic edge 

 of the pons or of the corpora quadragemina, authors 

 having adopted different usages. It will thus be seen that 

 the weight and volume of the cerebrum must be somewhat 

 greater in cases where the quadrigemina are still in con- 

 nection with it. In the case of the tables from Boyd, 

 which I shall present later, the term cerebrum means 

 the brain mass cephalad of the quadrigemina. When 

 the cerebrum is divided in the median plane, it is sepa- 

 rated into two symmetrical portions, the hemispheres. 

 To follow further the subdivisions which are sometimes 

 made, it will suffice to consider one of the hemispheres 

 alone. If the island of Reil, a sunken portion of the 

 hemisphere, be exposed by turning back the opercula 

 which cover it, and which are formed by the edges of the 

 parietal, frontal, and temporal lobes coming together 

 along the line of the Sylvian fissure, the part thus un- 

 covered is seen to be bounded by a continuous sulcus. 

 If a scalpel be carried through this sulcus cutting deeply, 



