THE PINEAL AND PITUITAEY BODIES 



209 



The optic thalamus, which lies at the side of the third ventricle 

 and forms part of the floor of the lateral ventricle, is covered externally 

 by a layer of white fibres, most marked next to the internal capsule, 

 fibres from which pass into the thalamus and serve to connect it with 

 the hemisphere. 



The grey matter of the thalamus (fig. 244) is partially subdivided 

 by an oblique white lamina into a smaller, inner (/), and a larger, 

 outer, nucleus (e)\ these contain a number of small scattered iierve- 

 cells. Anteriorly another portion of grey matter (a) is divided off in a 

 similar way ; this contains comparatively large nerve-cells. 



Attached to the optic thalamus below and externally are the two 

 gcniculate, bodies which are connected with the optic tract. The outer 

 geniculate body has a lamellated structure consisting of alternating 

 layers of grey and white matter. 



The tegmentum of the crus cerebri is prolonged below the thala- 

 mus opticus into a mass of grey substance, with longitudinally and 

 obliquely crossing white bundles, which is known under the name of 

 subthalamic region. In it at least three parts differing from one 

 another in structure may be distinguished (see fig. 244, i, 2, 3). 



The pineal gland, which is developed in the roof of the third 

 ventricle, is composed of a number of tubes and saccules lined and 

 sometimes almost tilled with epithelium, and containing deposits of 

 earthy salts (brain sand). These may, however, occur in other parts 



FIG. 246. SECTION OF THE UPPER PART OF THE BRAIN AND MENINGES TO SHOW THE 



RELATIONS OF THE ARACHNOIDAL VILLI. (Magnified.) 



c.c. corpus callosum ; /, falx cerebri ; s.a. subarachnoid space, pervaded by a network of 

 fine trabeculee ; from it the fungiforai villi are seen projecting into the dura mater. 

 Some are projecting into the superior longitudinal sinus, s. 



of the brain as well. The follicles are separated from one another by 

 vascular connective tissue derived from the pia mater. 



The pituitary body is a small reddish mass which lies in the sella 



