318 NERVOUS SYSTEM. 



wind in its course like a horn, has got the name of the inferior 

 cornu. From the superior part of the cavity, another flexuous 

 passage, smaller than the former one, taking a direction at first 

 outward, then downward, and lastly forward, leads to the base of 

 the brain, through the substance of the middle lobe, and there 

 ends in a blind termination : from which circumstance, and from 

 its cylindroid figure, some call it the digital cavity, others the 

 superior cornu. The two ventricles are lined (and the parts 

 within them covered) by an extension of pia mater, which finds 

 its way into them along with the vessels forming the choroid 

 plexus. By this membrane, whose vascularity appears to be 

 lower than that of the pia mater elsewhere, the watery fluid, it is 

 supposed, is secreted : unlike serous cavities in general, however, 

 the ventricles appear to hold water during life; for, if an animal 

 is put to death suddenly, and these cavities are opened with all 

 possible expedition, water, and not vapour, is uniformly found 

 contained. 



Contents. — We now come to what are considered as the con- 

 tents of the lateral ventricles. They are — the corpora striata, 

 the hippocampi, the plexus choroides, the fornix, and the thalami 

 nervorum opticorum. But a view of all these parts cannot be 

 obtained until we have reflected the corpus callosum ; prior to 

 which being done, that body should be cautiously raised, in order 

 to shew the 



Septum Lucidum, the translucent medullary partition between 

 the ventricles, which extends perpendicularly along the corpus 

 callosum in front, and is attached to the fornix behind. It is 

 broad inferiorly, grows gradually narrow superiorly, where it ends 

 in a point, at the angular junction of the corpus callosum with 

 the fornix. It consists of two thin laminse of medullary matter, 

 included between and supported by the membranous linings of 

 the ventricles, in the middle of which is a fissure or small cavity, 

 by some described as the ffth ventricle, but more generally 

 known as the fossa Sylvii. Sometimes this fissure is very de- 

 monstrable, glistening interiorly with moisture ; at other times it 

 is hardly perceptible. 



Corpora Striata. — When the corpus callosum is turned back, 

 four large and remarkable eminences present themselves, two 

 upon each side of the septum lucidum. The two inferior, and 

 most bulky, are the corpora striata. They rise out of the lower 

 and back parts of the ventricles, projecting into the middle of the 

 cavities, where they become broad and approach the septum ; 

 growing narrow and receding from each other, above ; below, 

 extending along the anterior cornua. Externally, they have a 



