610 



THE NEKVOUS SYSTEM. 



(Fig. 538). It is a large ovoid mass of gray matter, which lies obliquely aero 

 the path of the cerebral peduncle as it descends from the cerebral hemisphei 

 The smaller anterior end of the thalamus lies close to the median plane, and 

 separated from the corresponding part of the opposite side only by a very narro 

 interval. The enlarged posterior ends of the two thalami are placed more wide' 

 apart, and in the interval between them the corpora quadrigemina are situated. 



The two thalami, in their anterior two-thirds, lie close together, one on each si( 

 of the deep median cleft which receives the name of the third ventricle of tl 

 brain. The inferior and lateral aspects are in apposition with, and, indeed, direct 

 connected with, adjacent parts of the brain, and on this account it is customary 

 study them by means of sections through the brain. The superior and medi 

 surfaces are free.' 



The lateral surface of the thalamus is applied to a thick layer of white matt 



interposed b 

 tween it and t] 

 lentiform ni 

 cleus, called tl 

 internal capsu! 

 and composed 

 fibres passir 

 both upwards t 

 wards and dow: 

 wards from tl 

 cerebral corte 

 A large propo 

 tion of these fibr 

 descend to for 

 the basis pedu: 

 culi. From tl 

 entire extent 

 the lateral su 

 face of the thai 

 mus large nur 

 bers of fibn 

 stream out ai 

 enter the ii 

 ternal capsule, 

 reach the cer 

 bral cortex. Th< 

 constitute wh 

 is termed tl 

 thalamic radi 

 tion. As tl 

 fibres leave tl 



FIG. 539. THE THALAMI AND THE PARTS OF THE BRAIN SURROUNDING THEM. thalamus OV< 



Superior aspect. the whole of tl 



lateral surface of the ganglionic mass they form a very distinct reticulated zoi 

 or stratum, which is termed the external medullary lamina. 



The inferior surface of the' thalamus rests on the hypothalamus. From tl 

 latter region many fibres enter the thalamus on its inferior aspect, whilst oth 

 fibres leave this surface of the thalamus to take part in the thalamic radiation. 



The superior surface of the thalamus is free. Laterally it is bounded by 

 groove, which traverses the floor of the lateral ventricle of the brain ai 

 intervenes between the thalamus and the caudate nucleus. In this groo 

 are placed a slender band of longitudinal fibres, termed the stria terminal 

 and in its forepart the vena terminalis. Medially, the superior surface of t 

 thalamus is separated from the medial surface in its anterior half by i 

 sharp edge or prominent ledge of the ependyma of the third ventricle. This 

 termed the tsenia thalami, and the ridge which it forms is accentuated by t,J 



Non-ventricular 

 part of thalamus 



Groove 



corresponding 



to fornix 



Quadrigeminal 



bodies 



Trochlear nerve 



Brachium 



pontis 



Brachium 



conjuiictivum 



Lingula 



Medulla 

 oblongata 



Genu of corpus 

 callosum 

 Corpus callosum 

 (cut) 



Cavum septi 



pellucidi 



Septum pellucid urn 



Caudate nucleus 



Fornix 



Foramen inter- 

 ventriculare 



Anterior commissure 

 Anterior tubercle 

 of thalamus 



Massa intermedia 



Third ventricle 



Stria terminalis 



Tsenia thalami 



Trigonum habenulse 



Posterior 



commissure 



Stalk of pineal body 



Pulvinar 



Pineal body 



