THE PINEAL AND PITUITARY BODIES. 243 



nerves. Many, at least of the converging fibres, must stop short in 

 the gray matter of these ganglionic masses, or they would certainly 

 form a larger peduncle to each hemisphere than actually exists, and 

 no instance has been detected of two or more white fibres uniting, in 

 this situation, into a single one, and so accounting for their diminution 

 in number. The convergent or radiating fibres of the cerebrum exceed 

 the others in number ; but the large proportion which the commis- 

 sural fibres bear to them, appears to be one cause of the greater size 

 of the cerebra of the higher animals, and especially of that of man. 



Besides the corpora striata, and the optic thalami, other smaller 

 masses of mixed gray and white matter demand attention. Thus, on 

 the under surface of each frontal lobe, is found a small elongated ob- 

 long mass of gray matter called the olfactory lobe, which is attached 

 by a narrow white peduncle, spreading backwards into three bundles, 

 to the under surface of the frontal lobe, and to certain adjacent parts 

 at the base of the cerebrum, in front of the Sylvian fissure ; it is from 

 these olfactory lobes, that the proper olfactory nerves, or nerves of 

 smell, are given off to the nose on each side. Again, resting on the 

 back part of the conjoined cerebral peduncles, overhung by the pos- 

 terior border of the corpus callosum, and attached by white fibrous 

 nervous substance, to the optic thalami, to the cerebellum, to the cere- 

 bral peduncles, and to the medulla oblongata, are four small emi- 

 nences, named the corpora quadrigemina, two on each side of the 

 middle line, and all blended together. They are white on their sur- 

 face, but are composed of gray matter intermixed with many white 

 fibres, running transversely, obliquely, and longitudinally : it is from 

 these that the optic tracts, or roots of the optic nerves, or nerves of 

 sight, chiefly take their origin. Two other little gray masses on each side, 

 named corpora geniculata, are also found in connection with the tract 

 or root of each optic nerve. Supported above the corpora quadri- 

 gemina, is a little conical body, attached by minute white pedicles, to 

 the surface of the optic thalami ; it is named the pineal body or pineal 

 gland, and was supposed by the celebrated Des Cartes to be the seat 

 of the soul. It is larger in the child and in the female, than in the 

 male; it contains two or more cavities, usually filled with a viscid 

 fluid, and .gritty matter, acervulus cerebri, composed chiefly of aggre- 

 gations of the so-called amyloid bodies, mixed with earthy and a little 

 animal matter. The substance of the pineal body, contains pale 

 roundish cells, and a few nerve fibres. Lastly, projecting downwards 

 from the base of the brain, between the diverging cerebral peduncles, 

 and connected with the floor of the ventricular cavities, is a tubular 

 peduncle, which supports a nut-shaped mass, named the pituitary body 

 or hypophysis cerebri. It weighs from five to ten grains, and, in the 

 adult, is solid and firm. It is composed of an anterior larger, and a 

 posterior smaller and deeper colored lobe, both, however, being very 

 vascular. The anterior lobe especially, has been found to present a 

 structure resembling, somewhat closely, that of the thyroid body, which 

 is one of the so-called ductless glands. (Sharpey.) In the posterior 

 lobe, a few nerve tubes are found. The use of this body, and that of 

 the pineal gland, are entirely unknown. 



