612 



THE NEKVOUS SYSTEM. 



From the lateral nucleus by far the greatest number of the fibres which form the 

 radiatio thalami pass, and these are seen crossing it in various directions towards 

 the lamina medullaris externa. The anterior nucleus (nucleus anterior thalami) is 

 the smallest of the three thalamic nuclei. It forms the prominent anterior tubercle, 

 and is prolonged in a wedge-shaped manner, for a short distance, downwards and 

 backwards between the anterior parts of the medial and lateral nuclei. The internal 

 medullary lamina splits into two parts and partially encloses the anterior nucleus. 

 In connexion with its large cells a very conspicuous bundle of fibres, the fasciculus 

 thalamomamillaris, comes to an end. [As this bundle arises in the corpus 

 inamillare, it ought to be called "fasciculus marnillo-thalamicus."] 



A diffuse gray mass, imperfectly marked off from the inferior surface of the lateral nucleus, 

 receives the name of the ventral nucleus. Its inferior part is composed of the central nucleus oi 

 Luys and the nucleus arcuatus. In section the former appears as a circular mass of gray matter, 

 which comes into view immediately behind the point where the internal medullary lamina 

 disappears. It would seem to be intimately connected with fibres which reach it from the red 

 nucleus and from the posterior commissure. These fibres pass round it so as to mark it off from 

 the rest of the thalamus, and in front of the nucleus many of them enter the internal medullas 

 lamina. The nucleus arcuatus is a small semilunar mass of gray matter placed below and to the 

 lateral side of the central nucleus of Luys. 



The connexions of the thalamus are of an extremely intricate kind. It would 

 appear to be a ganglionic mass interposed between the tegmental corticipetal tracts 

 and the cerebral cortex. In its posterior part, and through its stratum zonale, it alsc 

 has important connexions with the optic tract. The corticipetal tegmental tracts 

 which enter it from below, will be noticed in connexion with the hypothalamic 



region. Suffice it to say, for the 

 present, that these fibres end in the 

 midst of the thalamus in connexion 

 with the thalamic cells. In additior 

 to these, enormous numbers of fibres 

 arising within the thalamus as th( 

 axons of its cells, stream out from it: 

 lateral and inferior surfaces to forn 

 the thalamic radiation. Thes< 

 thalamo-cortical fibres pass to ever 

 part of the cortex ; and althougl 

 there is no separation of them int 

 distinct groups as they leave th 

 thalamus, it is customary to regari; 

 them as constituting a frontal stall 

 a parietal stalk, an occipital stall 

 and a ventral stalk. But fibres fror j 

 the cortex, cortico- thalamic fibre 

 likewise stream into the thalamu 

 in large numbers, and end in fir 

 arborisations around its cells, 

 double connexion with the cerebrr 

 cortex is thus established by tl 

 thalamus. 



The frontal stalk of the thalanr 

 radiation emerges from the anterior pa 

 of the lateral surface of the thalamus ai 

 passes through the anterior limb of t ' 

 FIG. 540. -SCHEMA. Founded on the observations of internal capsule to reach the cortex of 1 1 



CORP. CALLOSUM 



ANT9 LIMB 

 NTtCAPSUUr 



CORP:GEN:MED 



SUP QUADV BODY 



ME.6t4PEPHALON 



TEMPORO-PONTINE 

 TRACT 



Flechsig, and Ferrier and Turner. 



frontal lobe. Many of these hbres end 

 the caudate and lentiform nuclei, betwej 

 which they proceed. The parietal stalk issues from the lateral surface of the thalamus, ai 

 passing through the internal capsule (and to some extent, also, through the lentiform nucl( 

 and the external capsule), gains the cortex of the posterior part of the frontal lobe and of 1 ' 

 parietal lobe. The occipital stalk emerges from the lateral aspect of the pulvinar and constitu i 

 the so-called optic radiation. These fibres sweep laterally and backwards round the lateral s 

 of the posterior horn of the lateral ventricle to gain the cortex of the occipital lobe, ijf 



