616 HANDBOOK OF PHYSIOLOGY. 



The cells of the corpora striata are evenly distributed, and not 

 grouped in nuclei. Their neuraxons pass, for the most part, into the 

 internal capsule. The corpora striata are connected with the cerebellum 

 through these fibres. It is doubtful if these ganglia have any anatomical 

 relations with the cortex of the brain. 



Optic Thalami. The optic thalami are oval in shape, and rest 

 upon the inner and dorsal surfaces of the crura cerebri. The upper sur- 

 face of each thalamus is free, and of white substance; it projects into 

 the lateral ventricle. The posterior surface is also white. The inner 

 sides of the two 1 optic thalami form the outer borders of the third 

 ventricle, are in partial contact, and are composed of gray material un- 

 covered by white and are, as a rule, connected together by a transverse 

 portion. 



The optic thalamus is composed of several collections of gray matter, 

 forming somewhat indistinctly defined masses separated by white fibres. 

 These masses of gray matter are known as the nuclei of the thalamus, 

 and they are six in number. They are called the anterior tubercle, the 

 median nucleus, the lateral nucleus, the ventral nucleus, the pulvinar, 

 and the posterior nucleus. The anterior tubercle is composed of large 

 nerve-cells whose neuraxons pass down to the corpora mammillaria at the 

 base of the brain. There they meet the fibres of the fornix which con- 

 nect this tubercle of the thalamus with the hippocarnpal convolution. 

 The median nucleus is connected by its neuraxons with the cortex of the 

 Island of Eeil and the second and third convolutions. The lateral nu- 

 cleus is quite large and lies against the internal capsule, into which it 

 sends fibres. It is connected with the central convolutions. The ven- 

 tral nucleus lies beneath the preceding; it is small in size. It is con- 

 nected with the cortex of the frontal lobe and with the operculum, the 

 central convolutions, and the supramarginal gyms. The fifth nucleus, 

 known as the pulvinar, forms the posterior tip of the thalamus, and is 

 connected with the optic tract. The posterior nucleus, lying just below 

 the pulvinar, is a small mass and is connected with the cortex of the in- 

 ferior parietal convolution. The cells of the optic thalamus are thus 

 seen to be connected with a large area of the cerebral cortex. They are 

 also connected with the sensory, and probably, to some extent, with the 

 motor tracts coming from below. 



Corpora Quadrigemina. There are two on each side, anterior 

 and posterior; they form prominences on the dorsal surface of the pons 

 'and crura above the aqueduct of Sylvius. They are composed of alter- 

 nate layers of white and gray matter. The posterior bodies receive 

 fibres from the eighth nerve and the sensory tract, known as the 

 fillet. They send fibres out to the temporal region of the brain. They 

 are closely associated with the lateral corpora geniculata. The anterior 

 corpora quadrigemina are connected by fibres with the optic nerve and 



