156 OUTLINES OF EQUINE ANATOMY. 



and anteriorly and posteriorly presents somewhat firm union 

 of the hemispheres. It contains the falx cerebri, and is 

 terminated below by a layer of white matter, corpus cal- 

 losum, which connects the two hemispheres, and is com- 

 posed of fibres which run transversely from the white 

 substance of the hemispheres, the anterior fibres being 

 curved forwards, the posterior backwards, so that the nar- 

 rowest portion is that shown by separation of the two 

 hemispheres without incision. On its upper surface may 

 be distinguished a central longitudinal line, the rop/ie, 

 along which arteria corporis callosi passes, and on each 

 are the linese longitudinales laterales, while lineae trans- 

 versae intersect these at right angles. The corpus callosum 

 terminates both anteriorly and posteriorly by a rounded 

 extremity ; the anterior is the genu, the posterior the 

 splenu. From the latter the fornix runs in a forward 

 direction, connecting together the hippocampi. Anteriorly, 

 at the foramen of Munro, the fornix terminates in four 

 crura. The anterior run to the base of the brain, where 

 they terminate in the single corpus albicans (there are 

 two in the human subject). The posterior take the name 

 of corpora fimbriata, and extend into the posterior cornua 

 of the lateral ventricle. The upper surface of the fornix 

 is connected to the under surface of the corpus callosum 

 by the septum lucidum, a thin layer of nerve matter which 

 separates the lateral ventricles one from the other, and 

 between the two layers of which is the fifth ventricle (which 

 we have never found in the horse). By removing a small 

 layer from the upper surface of the cerebral hemispheres 

 we may demonstrate that they are composed externally of 

 grey matter, internally of white. The grey matter, cine- 

 ritious, is of uniform thickness throughout, but since it 

 invests the convolutions presents a wavy margin. The 

 white or medullarij matter in this section is termed the 

 centrum ovale minor, and presents the cut extremities of 

 vessels, through which, in the fresh subject, a small 

 quantity of blood oozes, puncta vasculosa. If sections are 

 now made through both hemispheres on a level with the 

 corpus callosum, the whole of the upper surface of that 

 layer or ceiitrum ovale major is exposed. By incision 

 through this on either side we lay open the cavity of the 

 lateral ventricle, a space divisible into anterior and pos- 

 terior cornua, bounded anteriorly and externally by the 



