Til K Til A LAM I 'S 861 



passing between the two through the internal capsule directly, and by 111 ires curving 

 from below, chielly from the lateral and medi:il nuclei, and passing in the ansa lentii- 

 ularis. 



The cortical connections of the thalamus are abundant. They cons'. 

 fibres both to and from the cortex of the different lobes of the hemisphere, the greater 

 part arisinir in the thalamus and terminating in the cortex. These fibres collect in 

 the internal and external medullary laniitue and the stratum zonale; ir.c.st of them 

 enter the internal capsule and thence radiate to the different parts of the cortex. 

 They form the so-called peduncles of the thalamus. which have been distinguished 

 both by the Flechsig method of invest igat ion and by the method of degeneration. 

 The anterior or frontal peduncle pusses from the lateral and anterior part of the 

 thalamus through the frontal portion of the internal capsule, and radiates to the 

 cortex of the frontal lobe. The middle or parietal peduncle passes from the lateral 

 surface of the thalamus through the intermediate part of the internal capsule, and 

 upwards to the cortex of the parietal lobe. The posterior or occipital peduncle 



i chiefly from the pulvinar, through the occipital portion of the internal ca| Mile. 

 and radiates backwards to the occipital lobe by way of the occipito-thalamic (optic) 

 radiation (fig. 643). The inferior peduncle passes from the inner and under surface 

 of the thalamus (from the anterior part chiefly), turns outwards to course beneath 

 the lenticular nucleus, and radiates to the cortex of the temporal lobe and insula. 

 Many of the fibres of this peduncle course in the ansa lenticularis (fig. 641). Some 

 turn upwards in the external capsule to reach the cortex above the insula. 



The hypothalamic nucleus, or body of Luys, is the principal nucleus of termi- 

 nation of the medial lemniscus, the great sensory cerebro-spinal pathway. It con- 

 tains the cell-bodies of the neurones of the third order in this pathway, those of the 

 first order being situated in the spinal ganglia, and those cf the second order in the 

 nuclei of the fasciculus gracilis and fasciculus cuneatus. It is a biconvex mass of 

 grey substance situated below the lateral and anterior nuclei of the thalamus, and 

 between these and the basis of the cerebral peduncle, or rather the substantia nigra, 

 which is spread upon the dorsal surface of the peduncle, and which, though greatly 

 diminished, extends into the hypothalamic region. The hypothalamic nucleus pre- 

 sents a brownish-pink colour in fresh material, due to pigment in its cells and to 

 its abundant capillary supply. It is enclosed by a thin capsule of white substance, 

 some of the fibres of. which seem to decussate with those of the opposite side in the 

 floor of the third ventricle, above and just behind the region of the corpora mammil- 

 laria. By far the greater part of the fibres arising from the nucleus join the internal 

 capsule, and through it ascend to radiate to the cortex of the pre- and post-central 

 gyri, the sensory-motor or somaesthetic area of the hemisphere. 



All the fibres connecting 1 he cere.bral cortex with both the thalamus and the hypo- 

 thalamic nucleus belong to the so-called projection fibres of the cerebral hemisphere. 



Worthy of note here are two other structures which, like the thalamus, belong 

 to the thahunencephalic portion of the dieneephalon, though mention of them and 

 their connections has been deferred because of the fact that they are encountered in 

 sections for the internal structure of the telencephalon, since, as usually studied, 

 such sections are made to involve both the telencephalon and the dieneephalon. 

 These structures are the liabenular nucleus and the fasciculus retroflcxus of Meynert. 



The habenular nucleus, a part of the epithalamus, is a small group of nerve 

 cells situated in the substance just below and lateral to the epiphysis. A ;-mall 

 bundle of fibres crossing the mid-line under the epiphysis in the dorsal aspect of the 

 posterior cerebral commissure has been called the commissura habenularum, frcm 

 the fact that it apparently connects the habenular nuclei of the two sides. 



The fasciculus retroflexus (Meynerti) is a relatively strong bundle of medul- 

 lated ii!>res which runs ventralwards and slightly caudal\\ ards from the habenular 

 nucleus towards the inferior portion of the interpeduncular fossa. It has been 

 shown that many, at least, of the fibres of this bundle arise from (lie cells of the 

 habenular nucleus. In its slightly caudad course, the bundle passes obliquely 

 through the red nucleus, entering the mesial sii[>erior aspect and making its exit 

 from the ventro-mesial side of the inferior extremity of this nucleus. In the animaN 

 in which it has been studied, the bundle seems to terminate in the interpedunculur 

 t/nni/Unii. a group of nerve cells lying in the floor of the interpeduncular fossa at 

 the level of the inferior quadrigemina. In man, the interpeduncular ganglion is 

 seemingly absent as such, and the bundle seems to disappear in the posterior per- 



