1420 A MANUAL OF ANATOMY 



matter enter the optic radiation as corticipetal j5bres. The lateral 

 or outer geniculate body is associated with the visual sense. 



The corpus geniculatum internum is a small oval eminence, which 

 is situated below the pulvinar and on the lateral aspect of that 

 portion of the mesencephalon which constitutes the corpora quadri- 

 gemina. The inferior brachium, which is beneath it, connects it 

 with the lower quadrigeminal body. • 



The inner geniculate body contains many nerve-cells, the axons 

 of which become corticipetal fibres, their destination being the 

 cortex of the temporal region of the brain. Through means of the 

 lower quadrigeminal body and the internal brachium the inner 

 geniculate body receives fibres from the lateral or acoustic fillet, 

 which terminate in arborizations around its cells. The axons of 

 these cells become corticipetal fibres, the destination of which is 

 the cortex of the temporal region of the brain. The inner genicu- 

 late body is associated with the auditory sense. 



Development. — The corpora geniculata appear as elevations on the lateral 

 wall of the thalamencephalon or diencephalon. 



Structure of the Optic Thalamus. — The optic thalamus is composed chiefly 

 of grey matter. Its superior surface is covered with a layer of white matter, 

 known as the stratum zonule, and its lateral surface is covered with a reticular 

 layer of white matter, called the external medullary lamina. The mesial 

 surface has a thick coating of grey matter which is continuous with the grey 

 matter around the aqueduct of Sylvius. 



The grey matter of the interior of the optic thalamus is traversed by a 

 plate of white matter, called the internal medullary lamina, which divides it 

 into two nuclear areas — lateral and mesial. The lateral nuclear area lies 

 between the internal and external medullary laminae, and extends backwards 

 as far as the pulvinar. The mesial nuclear area Ues between the internal 

 medullary lamina and the thick layer of grey matter which coats the mesial 

 surface of the optic thalamus. It extends backwards as far only as the 

 habenular region, and anteriorly it is separated from the anterior tubercle 

 by a lamina of white matter. The region of the anterior tubercle therefore 

 constitutes a third or anterior nuclear area of grey matter. The grey nuclear 

 areas are consequently three in number — lateral, mesial, and anterior. 



Lateral Nuclear Area. — This area includes the pulvinar, the geniculate 

 bodies, and the radiate nucleus. The pulvinar and geniculate bodies have 

 just been described. The radiate nucleus is associated with the fibres of the 

 thalamic radiation, to be presently referred to. 



Anterior Nuclear Area. — This area includes the anterior tubercle, and is 

 the chief sensory nucleus. It receives corticifugal fibres, and its cells furnish 

 corticipetal fibres. It also receives many of the fibres of the lateral fillet, as 

 well as those of the superior cerebellar peduncle, and the fibres of the bundle 

 of Vicq d'Azyr. 



Mesial Nuclear Area. — ^This area contains the ganglion habenul^e, to be 

 presently described. 



Connections of the Optie Thalamus. — (i) Viewing the optic thalamus as an 

 aggregation of ' cell-stations ' in the course of the centripetal fibres of the 

 tegmentum of the crus cerebri, the tegmental fibres probably all terminate in 

 the thalamic cells. (2) Through means of the stratum zonale the optic 

 thalamus is connected with the optic tract and optic radiation. (3) The 

 cells of the anterior nucleus receive the fibres of the bundle of Vicq d'Azyr, 

 which are continuous, through the corpus albicans, with the fibres of the 

 anterior pillar of the fornix. (4) Thalamic Radiation. — This is composed 

 of thalamo-cortical fibres which arise within the optic thalamus as the axons 

 of the thalamic cells. They issue from its external and inferior surfaces, 

 and pass to all parts of the cerebral cortex. They are conveniently arranged 



