CORPUS STRIATUM. CHOROID PLEXUS. 413 



below (floor) by the following parts, taken in their order of position 

 from before backwards : 



Corpus striatum, 

 Tenia semicircularis, 

 Thalamus opticus, 

 Choroid plexus, 

 Corpus fimbriatum, 

 Fomix. 



The Corpus striatum is named from the striated lines of white and 

 grey matter which are seen upon cutting into its substance. It is 

 grey on the exterior, and of a pyriform shape. The broad end, direct- 

 ed forwards, rests against the corpus striatum of the opposite side : 

 the small end, backwards, is separated from its fellow by the interpo- 

 sition 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 medul- 

 lary substance, extending along the posterior border of the corpus 

 striatum, and serving as a bond of connection 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, which terminates in the vena Galeni 

 of its own side. The vein is overlaid by a yellowish band, a thick- 

 ening 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 Tlialamus opticus (thalamus, a bed) is an oblong body, having 

 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. Part 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 (%ogiov, i/3o;, resembling the chorionf) is a vas- 

 cular fringe extending obliquely across the floor of the lateral ventricle, 

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

 ing, and communicates with the choroid plexus of the opposite ventri- 

 cle, through a large oval opening, the foramen of Monro, or foramen 

 commune anterius. 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 communication transversely between the lateral ventricles, and 

 perpendicularly with the third ventricle. 



* Peter Tarin, a French anatomist : his work, entitled " Adversaria Anato- 

 lica," was published in 1"50. 

 t See the note appended to the description of the choroid coat of the eye- 



nil 



mica, 



t i 



ball. 



