NEUROLOGY. 115 
each lateral ventricle, we commence with the corpus striatum, a pear-shaped 
eminence situated in the anterior horn, the obtuse extremity directed for- 
wards and inwards. Posteriorly the body is apparently prolonged back- 
wards into the inferior cornu of the lateral ventricle by a long tapering 
process, which terminates there. Internal and posterior to the corpus 
striatum is the optic thalamus, a gangliform body of greyish color. These 
two bodies are separated from each other by a superficial groove, in which 
lies a delicate band of fibrous matter, the tenia semicircularis, which is 
covered by a lamina of horny-looking matter, the lamina cornea. 
The choroid plexus is a fold of thin and very red vascular membrane 
derived from the pia mater, which enters the inferior cornu by the great 
cerebral fissure, and ascending, turns inwards just behind the septum luci- 
dum and anterior pillars of the fornix, and unites with its fellow of the 
opposite side, covering and nearly concealing from view the optic thala- 
mus. 
In the posterior cornu, there is seen in its internal wall a projection 
upwards of one of the convolutions, to which the name of hippocampus 
minor has been given. It is traversed by a deep furrow. In the descend- 
ing horn is a remarkable prominence, the hippocampus major, projecting into 
it from the inferior wall and following the curve of the horn. Beneath this- 
is a peculiar grey matter, connected with the hippocampus, known as fascia 
dentata. A thin margin from the fornix which overlaps the pie a a 
is called the corpus fimbriatum. 
The fornix is a white, fibrous, triangular arch or vault, convex above, situ~ 
ated horizontally beneath the corpus callosum and septum lucidum; it lies 
on the velum interpositum and choroid plexuses, and over the third ventricle. 
The base, posteriorly, arises by two long flat bands (the posterior pillars or 
crura), one from either side, by three roots, from the hippocampus major and 
minor and from the tenia hippocampi; these crura unite to form the body 
of the fornix, which bending forwards divides into two short round cords, 
the anterior pillars of the fornix. The inferior surface of the fornix is marked 
posteriorly with several fine oblique lines (/yra or corpus psalloides); although 
described as single it is really double, and divisible throughout except 
where the lyra unites opposite sides. It may be called the great inferior 
commissure of the cerebrum, the corpus callosum constituting the great 
superior commissure. The anterior pillars of the fornix bound a space in 
front, through which the lateral ventricles communicate with each other 
dhinwinah the foramen commune anterius. 
The third ventricle. If the fornix be divided transversely at abehind its 
middle, and the segments reflected, the velum interpositum being removed, 
a fissure known as the third ventricle, and situated between the optic thalami, 
will be exposed. Anteriorly and between the anterior pillars of the fornix 
this fissure is limited by a band of white matter called the anterior commis- 
sure. At its posterior extremity the third ventricle becomes much con- 
tracted in all its dimensions, and is continuous with a canal (aqueductus 
Sylvw) which leads to the fourth ventricle. The roof of the third ventricle 
is formed by the velum interpositum. | 
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