480 NEUROLOOr. 



LATERAL VENTRICLES. 



When the corpus callosum is cut through, two large cavities in 

 the substance of the hemispheres, the lateral ventricles^ are 

 exposed. These cavities are lined with a delicate" membrane, 

 covered with ciliated epithelium, which secretes a serous liquid 

 similar to the spinal fluid. They are each possessed of a roof 

 and two small recesses or comua. The roof of the body of the 

 ventricle is formed by the corpus callosum, and the Jioor by the 

 corpus striatum in front, and the internal part of the hippo- 

 campus behind ; while the septum lucidum stretches as a 

 partition between the two ventricles. Running obliquely from 

 behind forwards, and from without inwards, between the corpus 

 striatum and the hippocampus, is a furrow in which a red 

 vascular fringe, the choroid plexus, is lodged ; and between the 

 corpus striatum and the thalamus opticus is a narrow band of 

 "white matter, the tcenia semicircularis. 



The anterior cornu stretches from the body of the ventricle 

 into the anterior lobe of the cerebrum, and is continued as a 

 straight canal to the cavity of the olfactory lobe. The descend- 

 ing cornu passes backwards, outwards, and downwards, and 

 then forwards and inwards, thus winding round the optio 

 thalamus and crus cerebri, to terminate in a cul-de-sac in the 

 great lobe, near the fissure of Sylvius. As there are no posterior 

 lobes to the cerebrum of quadrupeds, so the posterior cornu of 

 the lateral ventricle, which is found in man, is also wanting. 



The septum lucidum is the thin, semi-transparent substance 

 which stretches between the corpus callosum above and the fornix 

 below, and forms the partition between the lateral ventricles. 

 It is triangular in shape, and in man is said to be composed of 

 two laminae, between which a perfectly isolated cavity, lined 

 with epithelium and containing a serous fluid, is found. This 

 cavity is the fifth ventricle, or ventricle of the septum iucidum ; 

 it appears to be wanting in the domesticated animals. 



The fornix is the longitudinal band which extends as au 

 arch along the lower border of the septum lucidum, and is 

 attached to the posterior extremity of the corpus callosum. It is 

 made up chiefly of white matter, and consists of a body and four 

 pillars. The body is triangular in form, broad and flat behind, 

 and narrow in front, where it dips down to leave the corpus 

 callosum ; its edges reach the choroid plexuses, and its inferior 



