CORPUS STRIATUM CHOROID PLEXUS. 369 



The Corpus striatum is named from the striated lines of white 

 and gray matter which are seen upon cutting into its substance. It 

 is gray on the exterior, and of a pyriform shape. The broad end, 

 directed forwards, rests against the corpus striatum of the opposite 

 side : the small end, backwards, is separated from its fellow by the 

 interposition of the thalami optici. The corpora striata are the 

 superior ganglia of the cerebrum. 



The Tenia semicircularis (tenia, a fillet) is a narrow band of 

 medullary substance, extending along the posterior border of the 

 corpus striatum, and serving as a bond of connexion between that 

 body and the thalamus opticus. The tenia is partly concealed by 

 a large vein (vena corporis striati) formed by small vessels from the 

 corpus striatum and thalamus opticus. and terminating in the venae 

 Galeni. The vein is overlaid by a yellowish band, a thickening of 

 the lining membrane of the ventricle. This was first noticed and 

 described by Tarinus, under the name of the horny band. We may, 

 therefore, term it tenia Tarini.* 



The Thalamus opticus (thalamus, a bed) is an oblong body, hav- 

 ing a thin coating of white substance on its surface ; it has received 

 its name from giving origin to one root of the optic nerve. It is the 

 inferior ganglion of the cerebrum. The border only of the thalamus 

 is seen in the floor of the lateral ventricle. We must, therefore, 

 defer its further description until we can examine it in its entire 

 extent. 



The Choroid plexus (%opov, sTSog, resembling the chorionf) is a vas- 

 cular fringe extending obliquely across the floor of the lateral ven-: 

 tricle, and sinking into the middle cornu. Anteriorly, it is small and 

 tapering, and communicates with the choroid plexus of the opposite 

 ventricle, through a large oval opening, the foramen of Munro. This 

 foramen may be distinctly seen by pulling slightly on the plexus, 

 and pressing aside the septum lucidum with the handle of the knife. 

 .It is situated between the under surface of the fornix, and the anterior 

 extremities of the thalami optici, and forms a transverse communi- 

 cation between the lateral ventricles, and below with the third 

 ventricle. 



The choroid plexus is variable in its appearance, and sometimes 

 presents groups and clusters of small serous cysts, which have been 

 mistaken for hydatids. 



The Corpus fimbriatum is a narrow white band, which is situated 

 immediately behind the choroid plexus, and extends with it into the 

 descending cornu of the lateral ventricle. It is Jjje lateral thin edge 

 of the 'fornix. 



The Fornix is a white layer of medullary substance, of which f a 

 portion only is seen in this view of the ventricle. 



The Anterior cornu is triangular in its form, sweeping outwards, 



* Peter Tarin, a French anatomist : his work, entitled " Adversaria Anatomica," was 

 published in 1750. 



t See the note appended to the description of the choroid coat of the eyeball. 



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