THE THALAMUS 



883 



The fibres from both sources enter it by way of the mammillo-thalamic fasciculus (figs. 671 and 

 695). The significance of this connection is mentioned in the description of the limbic lobe. 



The lateral nucleus, lying between the external and internal medullary lam- 

 inae, extends posteriorly to include the entire pulvinar. 



The pulvinar, as already noted, together with the lateral geniculate body, constitutes the 

 prosencephalic nucleus of termination of the optic tract, and the stratum zonale upon the surface 

 of this nucleus might be called the stratum opticum. The anterior portion of the la,teral 

 nucleus receives fibres inferiorly from the red nucleus, from the brachium conjunctivum 

 (cerebellum direct), and some fibres of the medial lemniscus terminate about its cells. 



The medial nucleus lies medial to the internal medullary lamina and forms the 

 posterior portion of the lateral wall of the third ventricle. It is shorter than the 

 lateral nucleus, and is less extensively pervaded by fibres. 



Fig. 695. — Coronal Section op Prosencephalon 

 OF Corpora Mammillaria. (Seen from in 

 Anatomy," Rebman, London and New York.) 



Lateral ventricle 

 (central portion) 

 Chorioid plexus ^ 

 of lateral ven- hX^ sv 



tricle ;--IS!!5# 



Caudate nucleus ^..{J- -'•'*'•'-' 



Massa inter- -^'^ 

 media 

 Internal capsule "■ 



Lenti- f Puta- ^ 



cular ! men 



nu- I Globus ^^ 



rieus 1 pallidus " 



External capsule — 



Claustrum '' 

 Ansa peduncu- 

 laris " 



Optic tract - 



Inferior peduncle .^ 



of thalamus 

 Inferior cornu of -' 

 lateral ventricle 

 Hippocampal i- 

 digitations 



Oculomotor nerve 



THROUGH ThALAMENCEPHALON AT ReGION 



front.) (After Toldt, "Atlas of Human 





Corpus callosum 



, Fornix 

 Third ventricle 



Thalamus 



Mammillo- 

 '' thalamic 

 fasciculus 



^Ansa lenticularis 



Hypothalamic 

 _ nucleus (corpus 

 Luysi) 



._ Substantia nigra 



.Basis of cerebral 

 peduncle 



Mammillary 

 body 



Interpeduncular 

 fossa 



Pons (Varoli) 



It is thought to receive fibres from the red nucleus, and perhaps some from the lemniscus, 

 and is usually continuous across the third ventricle with the opposite medial nucleus by the 

 massa intermedia. 



In comparative anatomy, the nuclei of the thalamus have been variously subdivided by 

 the different investigators. AU the nuclei are connected with the lenticular nucleus by fibres 

 passing between the two through the internal capsule directly, and by fibres curving from below, 

 chiefly from the anterior, lateral and medial nuclei, and passing inthe ansa lenticularis. 



The cortical connections of the thalamus are abundant. They consist of fibres 

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

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

 in the internal and external medullary laminae and the stratum zonale; most 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 investigation and by the degeneration method. The anterior or frontal 

 peduncle passes 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. (See fig. 700.) The 

 middle or parietal peduncle passes from the lateral surface of the thalamus through the inter- 

 mediate part of the internal capsule, and upward to the cortex of the parietal lobe. The pos- 

 terior or occipital peduncle passes chiefly from the pulvinar, through the occipital portion of the 

 internal capsule, and radiates backward to the occipital lobe by way of the occipito-thalamic 

 (optic) radiation (fig. 699). The inferior peduncle passes from the medial and basal surface 

 of the thalamus (from the anterior and medial nuclei chiefly), turns outward to course beneath 

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

 of this peduncle course chiefly in the ansa lenticularis (fig. 695). Some turn upward in the 

 external capsule to reach the cortex above the insula; others pass upward through the medullary 

 laminae of the lenticular nucleus. 



