256 - THE ANATOMY OF THE HORSE. 



striatum ; behind, another body of abont the same size, but white on 

 its surface — the hippocampus ; between the corpus striatum and the 

 hippocampus, a groove, in which there lies a red granular cord — the 

 choroid plexus. Where the hippocampus bounds this groove it is 

 margined by a white band — the taenia hippocampi ; and if the choroid 

 plexus be pulled gently backwards another white band will be seen to 

 margin the corpus striatum where it bounds the groove — this is the 

 taenia semicircular is} 



The anterior cornu is occupied by the base of the corpus striatum. 

 It curves downwards and forwards into the anterior part of the 

 hemisphere, where it communicates with the cavity of the olfactory 

 bulb. 



The descending cornu contains the prolongations of the hippocampus 

 and its taenia. It passes at first backwards and outwards, and then 

 curves downwards, forwards, and inwards, terminating at the base of 

 the hemisphere in the uncinate convolution. The ventricles are lined 

 by a ciliated epithelium, which is continuous through the foramen of 

 Monro with the lining of the 3rd ventricle. 



The Septum Lucidum is a thin, translucent partition between the two 

 lateral ventricles. It is broadest in front, where it is attached to the 

 rostrum, or reflected part of the corpus callosum. Its upper edge is 

 attached to the corpus callosum, and its lower edge to the fornix ; and 

 posteriorly these edges meet at an acute angle. The septum consists 

 of white matter in its centre, with a layer of grey matter on each side. 

 In man it contains a small isolated cavity — the 5th ventricle. 



The Fornix, or arch, is a mesially placed white band consisting of a 

 central part, or body, and two pairs of processes or pillars. The body 

 is flattened above and below, and broadest behind. Its upper face is 

 adherent posteriorly to the corpus callosum, but in front it dips down 

 and leaves beneath the forepart of the corpus callosum a space occupied 

 by the septum lucidum. The under surface of the body rests on the 

 velum interpositum, and at its anterior extremity arches over the 

 foramen of Monro. The anterior pillars of the fornix are two white 

 cords which descend in front of the foramen of Monro, being separated 

 by a slight interval. Reaching the base of the brain, they turn on 

 themselves, thus forming the corpus albicans, and they then enter the 

 optic thalamus. The posterior pillars are broader and natter, and not 

 so well defined. Each in part bestows its substance on the surface of 

 the hippocampus, and in part it descends along the anterior edge of 

 that body as the tcenia hippocampi, or corpus fimbriatum. 



1 The optic thalamus and taenia semicircularis are generally enumerated among the 

 objects visible in the body of the lateral ventricle. In the brain of the horse, however, 

 the choroid plexus completely conceals from view the optic thalamus, and in most cases 

 also the taenia semicircularis. 



