374 



THALAMUS OPTICUS. 



Fig. 170* 



it from the opposite ventricle ; and 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, 

 Fornix. 



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 exte- 

 rior, and of a pyriform shape. The 

 broad end, directed forwards, rests 

 against the corpus striatum of the op- 

 posite side : the small end, backwards, 

 is separated from its fellow by the in- 

 terposition 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 poste- 

 rior 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)^ which ter- 

 minates in the vena Galeni of its own side. The vein is formed by small 

 vessels from the corpus striatum and thalamus opticus, and 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, having a 



* The lateral ventricles of the cerebrum. 1, 1. The two hemispheres cut clown to a 

 level with the corpus callosum so as to constitute the centrum ovale majus. The sur 

 face is seen to be studded with the small vascular points puncta vasculosa; and sur- 

 rounded by a narrow margin which represents the grey substance. 2. A small portion 

 of the anterior extremity (genu) of the corpus callosum. 3. Its posterior boundary 

 (splenium); the intermediate portion forming the roof of the lateral ventricles has been 

 removed so as to expose completely those cavities. 4. A part of the septum lucid urn. 

 showing an interspace between its layers the fifth ventricle, f). The anterior cornu 

 of one side. 6. The commencement of the middle cornu. 7. The posterior cornu. 8. 

 The corpus striatum of one ventricle. 9. The tenia semicircularis covered by the vena 

 corporis striati and tenia Tarini. 10. A small part of the thalamus opticus. 11. The 

 d-ark fringe-like body to the left of the numeral is the choroid plexus. This plexus 

 communicates with that of the opposite ventricle through the foramen of Monro, or fo- 

 ramen commune anterius ; a bristle is passed through this opening (under figure 4), and 

 its extremities are seen resting on the corpus striatum at each side. The figure 1 1 

 rests upon the edge of the fornix, on that part of it which is called the corpus fimbria 

 turn. 12. The fornix. 13. The commencement of the hippocampus major descending 

 into the middle cornu. The rounded oblong body in the posterior cornu of the lateral 

 ventricle, directly behind the figure 13, is the hippocampus minor. 



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

 published in 1750. 



