860 



THE NERVOUS SYSTEM 



A horizontal section through the tccnia thalami, splitting the stria medullaris and 

 thus passing above the massa intermedia, shows the grey mass of the thalamus 

 divided into segments or nuclei by a more or less distinct internal medullary lamina. 

 This extends the whole length of the thalamus, dividing its middle and posterior 

 portion into the medial and the lateral nucleus. In front the lamina bifurcates 

 into a medial limb, extending to the medial surface of the thalamus, and a lateral 

 limb, extending forwards to join the genu of the internal capsule (fig. 641). This bi- 

 furcation results in a cup-like sheet of white substance which encloses the anterior 

 nucleus. On the external surface, next to the internal capsule, there may usually 

 be distinguished an external medullary lamina, separated from the white sub- 

 stance of the capsule by a reticular layer of mixed white and grey substance. 



The anterior nucleus, lying partially encapsulated in the bifurcation of the in- 

 ternal medullary lamina, is somewhat wedge-shaped and points backwards between 

 the front portions of the lateral and medial nuclei. It is composed chiefly of large 

 cells, and constitutes the anterior tubercle of the dorsal aspect. Its principal connec- 

 tion from below is with the nuclei of the mammillary body of the same and opposite 

 sides, and with fibres from the anterior columns of the fornix direct. The fibres from 



FIG. 641. CORONAL SECTION OF PROSENCEPHALON THROUGH THALAMENCEPHALON AT REGION 

 OF CORPORA MAMMILLARIA. (Seen from in front.) (After Toldt, "Atlas of Human Anat- 

 omy," Kebman, London and New York.) 



LATERAL VEXTRI- 

 CLE (VENTRAL 

 PORTION) 

 CHOKIOID PLEXUS 

 OF LATERAL VJtN- 

 TttlCLB 



CA UDA TE 

 NUCLEUS 

 MASSA 



INTERMEDIA 

 INTBRNAL 

 CAPSULE 



LEUTI- {PVTA 



xrciz t LOBVS 



KUCLE. 1 /M ,.,,,. 

 [ DUS 



EXTERNAL 

 CAPSULE 



CLAUSTRUM 

 ANSA PEDUN- 

 CULARIS 



OPTIC TRACT 

 INFERIOR PK- 

 DUSCLK or 

 TfiALA l/r\ 

 INFERIOR <"/:- 

 NU OF LATER- 

 AL VENTRICLE 

 IflPl'fK'AMI'Al. 

 VISITATIONS 



OCULOMOTOR 

 NER VE 





CORPUS 

 CALLOSUM 



FORNIX 



THIRD VEN- 

 TRICLE 



1 11M.AMUS 



I II ALAMO- 

 MAM. MIL- 

 LA I!)' FAS- 

 C1CUL US 



.I.V.svi l.EX- 

 TICVLARIS 



HYPOTHAL- 

 A.Vlr XL'- 



iCORPI'S 



i.rysi) 



SUHSTAXTIA 



MdRA 

 J1AS/S OF 



CKREHRAI. 



PEDUNCLE 

 CORPUS 



MAMMIL- 

 LA 1:1: 



,, INTER PE- 

 l>r.\'(.'ULAR 

 fOSSA 



PONS (VAROLII) 



both sources enter it by way of the thalamo-mammillary fasciculus (figs. 619 and 641). 

 The significance of this connection is noted in the description of the limbic lobe. 



The lateral nucleus, lying between the external and internal medullary lamina, 

 extends backwards to include the entire pulvinar, which, as already noted, together 

 with the lateral geniculate body, constitutes the prosencephalic nucleus of termina- 

 tion 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 lateral nucleus 

 also receives fibres below 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 inside the internal medullary lamina and forms the pos- 

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

 nucleus, and is less extensively pervaded by fibres. It is thought to receive fibres 

 from the red nucleus, and perhaps some from the lemniscus. and is usually con- 

 tinuous across the third ventricle with the opposite medial nucleus by the massa 

 intermedia. 



All the nuclei of the thalamus are connected with the lenticular nucleus by fibres 



