562 Dynamic Theory. 



and different individuals of the same tribe. In the horse it is placed 

 over the hind end of the third ventricle, above the corpora thalami, be- 

 tween the middle and the posterior commissures. In man it covers a 

 cavity called the common posterior foramen, which communicates down- 

 ward into the third ventricle. Its base is formed by a circular lamella, 

 or sheet of medullary matter, which is attached by its edges to the cir- 

 cumference of the cavity. From the lamella, in front, proceed two nar- 

 row white bands. These pass along towards the front in the fissure sep- 

 arating the two thalami, one of the bands being attached to each of the 

 thalami. When they reach the foramen of munro they become at- 

 tached to the anterior pillars of the f ornix, to be hereafter described. 



From the lower floor of the front end of the third ventricle there is a 

 diverticulum of the ventricular cavity which forms the cavity of a small 

 gray bulb called the Tuber Cinereum. It is single and median. Under- 

 neath and in front of the tuber cinereum is a funnel-shaped tube, its 

 base, or wide end, attached to the tuber cinereum, while its apex, or 

 small end, is attached to another bulb, the hypophysis or pituitary gland. 

 This tube is called the inf undibulum, or funnel. It is composed of gray 

 matter, and is very fragile. The hollow of the tuber cinereum is con- 

 tinued into it and ends there as a blind sac. The pituitary gland, which 

 is attached to the little end of the infundibulum, is composed of matter 

 almost amorphous, which, in the front part is yellow, and in the hind 

 part, brown. It is circular in shape, flattened above and below, and 

 differs in size in different subjects. It contains no cavity. It is at the 

 very bottom of the brain, and rests in a hollow of the sphenoid bone 

 called the sella turcica, or Turk's saddle. The front part is called the 

 anterior lobe, and the rear is the posterior. The former is the larger 

 and is concave behind, partly embracing the latter. In fishes, and other 

 low vertebrates, the cells of the walls of the pituitary body develop 

 into nerve cells and fibres, and it is joined to the rest of the brain as a 

 part of it, and is called the lobe of the infundibulum. Its function as 

 part of the active brain, appears to have backslid in man and the 

 higher vertebrates. 



The Cerebrum. This is the largest part of the brain in man and the 

 Mgher vertebrates. It is divided into two hemispheres by a deep fis- 

 sure, which cleaves the ends and the top from front to rear. Into this 

 fissure dips a fold of the dura mater, which, from its shape, is called 

 the f alx or sickle. It is accompanied by blood vessels. The posterior 

 end of the hemispheres in man and the apes, rests upon the cerebellum, 

 from which it is separated by an expansion of the dura mater, called the 

 tentorium. Each hemisphere is divided into three lobes, the anterior, 

 middle and posterior. The anterior is separated from the middle lobe 

 by a deep, transverse cleft called the fissure of Sylvius. In it is lodged 



