1 1 THALAM ENCEPHALON. 



front pass to the frontal lobe of the hemisphere ; those in the middle region 

 to the posterior part of the frontal and to the parietal lobe, besides some to the 

 temporal lobe; those behind partly to the temporal lobe, but chiefly to the 

 occipital lobe. The fibres to the occipital lobe pass out from the lateral margin of 

 the pulvinar, and have at first a curved course round the posterior horn of the 

 lateral ventricle, afterwards radiating, with a generally sagittal direction, towards 

 the cortex of the occipital lobe. They are often spoken of as the optic radiations. 

 These radiating fibres are continuous with others passing from the optic tract to 

 the pulvinar. The lower surface of the thalamus is continuous posteriorly with the 

 prolongation of the tegmentum (subthalamic tegmental region), but in front this 



Fig. 83. SECTION ACROSS THE OPTIC 



THALAMUS AND CORPUS STRIATUM 

 IN THE REGION OF THE MIDDLE COM- 

 MISSURE (E. A. S., after a prepara- 

 tion by Mr. S. G. Shattock). Natu- 

 ral size. 



tli, thalamus ; a^e,i, its anterior, ex- 

 ternal and internal nuclei respectively ; 

 iv, its latticed layer ; m.c. , middle com- 

 missure ; above and below it is the cavity 

 of the third ventricle ; c.c. , corpus callo- 

 suiu ; /, fornix, separated from the third 

 ventricle and thalamus by the velum 

 interpositum. In the middle of this are 

 seen the two veins of Galen and the 

 choroid plexuses of the third ventricle ; 

 and at its edges the choroid plexuses of 

 the lateral ventricles ; t. s., taenia semi- 



circularis : cr, forward prolongation of the crusta passing laterally into the internal capsule, i. c. ; 

 s. t. r., subthalamic prolongation of the tegmentum, consisting of (1) the dorsal layer, (2) the zona 

 inccrta, and (3) the nucleus of Luys ; s. n., substantia nigra ; n. c., nucleus caudatus of the corpus 

 htriatum ; n. I., nucleus lenticularis ; e. c., external capsule ; cl, claustrum ; /, island of Reil. 



prolongation inclines to the outer side and becomes lost in a layer of grey matter 

 which is continuous internally with the grey matter of the floor of the ventricle, 

 and is seen at the base of the brain as the anterior perforated lamina. At its anterior 

 end the thalamus merges into a tract of fibres which stream from it through the 

 internal capsule into the frontal lobe of the hemisphere (anterior stalk of thalamus'). 

 Other fibres curve downwards and outwards towards the white substance of the 

 hemisphere forming the so-called lower stalk of the thalamus (ansa peduncular is}. 

 Above this is another tract (ansa lenticularis), sweeping from under the thalamus 

 round the mesial part of the crusta to the lenticular nucleus of the corpus striatum. 

 The layer of grey substance which is interpolated between the two tracts may be 

 termed substantia interansalis ; including the two ansse it has been designated svb- 

 stantia innominata. 1 



The body of the thalamus is chiefly formed of grey matter with large and small 

 nerve-cells scattered in it, but their arrangement and connections with nerve-tracts 

 have not been satisfactorily ascertained. Its grey matter is partially subdivided into 

 two parts, the so-called inner and outer (mesial and lateral) nuclei of the thalamus 

 (Burdach), by a vertical white lamina, S-shaped in section (internal medullary 

 lamina). The lateral nucleus (e), is the larger and extends into the pulvinar ; it is 

 marked externally by the radiating white lines before mentioned as passing from 

 the thalamus into the inner capsule, and these confer upon its external layer some- 

 what of a reticulated aspect (latticed layer, w*). The mesial nucleus (i) does not 

 extend into the anterior tubercle, but this part of the grey substance of the 



1 The term "anse pedonculaire " was originally used (by Qratiolet) to include the whole substantia 

 innominata. 



