208 DISSECTION OF THE BRAIN. 



nerves, should be cut along the middle line, so that the left hemisphere can 

 be separated from the other. On the left hemisphere the crus of the fornix 

 is to be traced downwards through the gray matter of the third ventricle 

 to the corpus albicans, and then upwards into the optic thalamus. 



Anterior pillar of the fornix. The fornix begins in the thalamus near 

 the tubercle on the upper surface. From this spot it descends in a curved 

 direction to the corpus albicans, where it makes a turn like half of the 

 figure 8, and furnishes a white envelope to the gray matter of that body. 

 The crus then ascends through the gray substance in front of the optic 

 thalamus, and is applied to the like part of the opposite side to form the 

 body of the fornix. It is joined by bands of fibres from the Uimiu semi- 

 circularis and peduncle of the pineal body. 



The pineal body and the corpora qnadrigemina, which are placed be- 

 hind the third ventricle, may be next examined. 



Dissection. All the pia mater should be carefully removed from the sur- 

 face of the quadrigeminal bodies, especially on the right side, on which 

 they are to be seen. The posterior part of the hemisphere of the same 

 side may be taken away. 



The pineal gland (conarium) is a small conical body (fig. 68, g), which 

 is situate above the posterior commissure, and between the anterior pair 

 of the corpora quadrigemina. In shape like the cone of a pine, it is about 

 a quarter of an inch in length, and has the base or wider part turned for- 

 wards. It is connected to the optic thalami by two white bands, pedun- 

 cles of the pineal body ( /') : these begin at the base, and extending for- 

 wards, one on each side along the inner part of the thalamus, end by 

 joining the crura of the fornix. At the base of the gland is a band of trans- 

 verse white fibres which unites it which the posterior commissure. 



This body is of a red color and vascular, and incloses two or more cells 

 containing a thick fL:id, with amyloid bodies, and a calcareous material 

 (brain sand) consisting of particles of phosphate and carbonate of lime, 

 and phosphate of magnesia and ammonia * In its substance are large 

 pale nucleated cells. 



The corpora quadrigemina (fig. 68) are four small bodies, which are 

 arranged in pairs, right and left, and are separated by a median groove. 

 Each pair is situate on the upper aspect of the cerebral peduncle of the 

 same side. 



The anterior eminence (h, nates) is somewhat larger than the posterior, 

 from which it is separated by a slight depression ; it is oblong from before 

 backwards, and sends forward a white band to join the optic tract and 

 thalamus. 



The posterior eminence (<', testis) is rounder in form and whiter in 

 color than the preceding : it lias also a lateral white band which is directed 

 beneath the corpus geniculatum internum, and blends with the peduncular 

 fibres in the thalamus opticus. 



These bodies are small masses of gray substance enveloped by white, 

 and are placed on the band of the fillet which forms the roof of the aque- 

 duct of Sylvius. The processes (brachia) to the optic thalamus are acces- 

 sory parts to the peduncular fibres of the cerebrum (p. 209). 



billet oj the olivary body. If the upper margin of the cerebellum be 



1 These particles are referred to by Kolliker, as pathological products ; and the 

 concentrically arranged masses amongst them are said to be incrustations of fibrin 

 coagula. 



