422 STUDIES IN ADVANCED PHYSIOLOGY. 



of the soul, the soul being considered an individual and not 

 divisible into halves. Such speculation soon came to grief, 

 however, when it was discovered that this pineal gland was 

 relatively larger in the lower animals, and as greater dimen- 

 sions of soul were not to be attributed by these thinkers to 

 the brute creation, this view had to be abandoned. Its sci- 

 entific explanation is now, however, evident, it being noth- 

 ing more than the stump of an optic nerve which in the 

 early history of evolution connected with a third eye. All 

 traces of the eye are gone in all the higher animals, but the 

 proximal stump of the nerve is still present. In some of the 

 lower animals, certain forms of lizards, the pineal gland 

 still connects with a retinal structure, although even here it 

 has ceased to be functional. 



The surface of the cerebellum differs essentially from that 

 of the cerebrum. It has no true convolutions, although 

 marked by a series of transverse ridges. It is divided into 

 three lobes, a central or middle lobe and the two lateral 

 lobes. At the outer lower edge of each lateral lobe there is 

 a small added lobe called the flocculus. 



The Interior of the Brain. 



The Ventricles of the Brain. Before describing the 

 structures lying within the brain it seems desirable to show 

 the topography of the ventricles of the brain in order that 

 the other structures may be located with reference to these. 



The central canal of the spinal cord runs upward into the 

 medulla and here widens out into a large ventricle called 

 the fourth ventricle of the brain. This ventricle lies im- 

 mediately below the cerebellum. Instead of lying in the 

 center of the medulla it lies very close to the dorsal surface, 

 that is, next to the cerebellum, and separated from it by a 

 very thin wall only. This wall is easily torn and the inte- 

 rior of the ventricle laid bare. The width of the ventricle 

 here is considerable, a half inch or more. Proceeding up- 

 wards the ventricle again narrows into a small canal in the 

 mid-brain and as such a small canal passes entirely through 



