II26 



HUMAN ANATOMY. 



opposite side which descend within the tegmentum, lateral and ventral to the 

 posterior longitudinal fasciculus ; (3) fibres which cross to join the fasciculus retro- 

 flexus ; (4) fibres from the median fillet and (5) from the superior cerebellar 

 peduncle which traverse the commissure to reach the opposite thalamus ; (6) per- 

 haps fibres from the deeper gray stratum of the corpora quadrigemina to the cerebral 

 cortex of the other side. Its presence in all vertebrates and the very early 

 acquisition of a medullary coat by its fibres indicate, as pointed out by Edinger, 

 the fundamental character of the commissure. 



The Metathalamus. — This subdivision of the thalamencephalon includes em- 

 bryologically both the median and lateral geniculate bodies. • Since in the fully formed 



Fig. 974. 



Corpus callosum 



Fornix 



Choroid plexus 



Velum inter- 

 positura 



Nucleus habenulae 



Subthalamic 



nucleus 



Red nucleus 



Substantia nigra 



Oculomotor nerve 



Crusta of cerebral peduncle 



Caudate nucleus 



rhalamus 



Subthalamic region 



Choroid plexus in inferior 

 horn of lateral ventricle 



Caudate nucleus, tail 



Hippocampus, 

 obliquely cut 



Gyrus dentatus 



Gj'rus hippocampi, 

 bounding inferior 

 fissure leading into 

 choroidal plexus 



Frontal section of brain passing through thalami, subthalamic region and cerebral peduncles; inferior 

 horn of lateral ventricle with hippocampus in section also seen. 



brain the former are closely associated with the inferior colliculi and their arms, the 

 inferior brachia, they may be conveniently described in connection with the mid- 

 brain, as has been done (page mo). 



The lateral geniculate bodies, (corpora geniculata laterales), one on each side, 

 are two fusiform elevations, about 10 mm. in length and half as much in width, which 

 project from the outer and under surface of the posterior part of the thalamus (Fig. 

 958). They are so buried within the thalamus that they are much less distinct than the 

 median geniculate bodies. In front they receive the outer division of the optic tracts, 

 while behind they are connected by the superior brachia with the superior corpora 

 quadrigemina. In structure the lateral geniculate body consists of alternating layers 

 of white and gray matter. The former, somewhat thinner than the gray sul^stance, 

 is, to a large measure, the optic fibres, many of which end around the celb within 

 the gray lamince. Other fibres of the optic tract continue without interruption into 

 the superior brachium and so to the upper colliculus, while a certain number end 

 within the thalamus, and in their course over the surface of the latter take part in the 

 production of the stratum zonale (page 1118). From many of the cells within the 

 geniculate body, fibres proceed by way of the optic radiations to the cerebral cortex. 



