INTEKXAL PAllTS. 



541 



of the fornix, -which is a thin Layer of wliito braiii-substanee, broad 

 behind and narrow in front {fig. 378, 9) : external and anterior to this 

 is the clwroid j)hxus of the lateral ventricle (fig. 378, 10), a red vascular 

 fringe, forming the border of the velum intcrpositum, a fold of pia mater 

 extending inwards, on whicli the fornix rests : external and anterior to 

 the choroid plexus is the anterior and outward part of iheoj^tic thalamus, 

 appearing from beneath it (fig. 379, /) ; outside and in front of the 

 thalamus is the corjms striatum ; and between these two bodies is a 

 narrow flat band, the ttmia semicircular is. 



The anterior cornu (fig. 379, g) is the blind anterior extremity of 

 the ventricle, projecting a little way into the Avhite substance of the 

 frontal lobe. It is covered by the corpus callosum, and turns forwards 

 and outwards round the anterior free extremity of the corpus striatum, 

 descending as it proceeds, and bounded behind by that body, and 

 in ffont by the reflected part of the corpus callosum. 



The middle or descemlimj cornu turns round the back part of the optic 

 thalamus, which appears in its cavity and forms its anterior boundary, 

 while its remaining boundaries are formed by the hemisphere. At its 

 commencement it is directed backwards and outwards ; then, passing 

 downwards with a sweep, it curves forwards, and at its extremity has a 

 marked inclination inwards. The principal object seen upon the floor 

 of the cornu is the hij>pocam])us major (pes hippocampi or cornu 

 ammonis), a large white eminence extending the whole length of the 

 cornu (figs. 379, 381, G, C). The hippocampus major becomes enlarged 



Fig. 380.— A Deep View of 

 THE Lateual Ventricles 

 and theiu cornua ^yith the 

 Velum Interpositum. 4 



The fornix lias been divided 

 near its anterior jjillars and 

 turned back, c, tlie anterior 

 imrt of tlie corpus callosum 

 divided ; e, the lyra on the 

 lower surface of the corpus 

 callosum and forni.-v ; /, ante- 

 rior pillars of the fornix divided 

 (these are represented of toi 

 large a size); ;/, anterior, and 

 h, posterior cornu of the lateral 

 ventricle ; k, k, corpora striata ; q, 

 hippocampus major in the lower 

 part of the middle cornu ; r, r, 

 thalami optici ; s, s, taenia se- 

 micircularis ; t, t, choroid 

 plexus ; V, velum intcrpositum ; 

 X, X, posterior pillars of the 

 fornix ; y, eminentia collate- 

 ralis. 



towards its anterior and 



lower extremity, and is 



indented or notched on 



its edge, so as to present 



some resemblance to the paw of an animal, whence it has been called 



the pes hippocampi. The white fibres of its surface form only a thin 



