690 NERVOUS SYSTEM. 



Qualn assumes, from various researches, that, in new-born infants, the brain weighs 

 11-65 ounces, for the male, and 10 ounces, for the female. In both sexes, " the weight of 

 the brain generally increases rapidly up to the seventh year, then more slowly to between 

 sixteen and twenty, and again more slowly to between thirty-one and forty, at which 

 time it reaches its maximum point. Beyond that period, there appears a slow but pro- 

 gressive diminution in weight of about one ounce during each subsequent decennial period ; 

 thus confirming the opinion, that the brain diminishes in advanced life." 



The comparative weights of the several parts of the encephalon, calculated from 

 observations upon the brains of fifty- three males and thirty-four females, between the ages 

 of twenty-five and fifty-five, are as follows : 



The proportionate weight of the cerebellum to that of the cerebrum, in the male, is 

 as 1 to 8^, and in the female, as 1 to 8. 



The specific gravity of the whole encephalon is about 1036, that of the gray matter 

 being 1034, and of the white, 1040. 



The above weights are quoted from Quain's admirable work upon anatomy, and the 

 normal range of variations and averages only are given. When we come to treat of the 

 cerebrum and its relations to intelligence, we shall discuss the weights of the brain in 

 idiots and in persons of extraordinary intellectual power, as far as any data upon these 

 points are to be found. 



Some Points in the Physiological Anatomy of the Encephalon and its Connections. 

 The direction of the fibres in the encephalon, their connections with the cells of the 

 gray substance, the course of commissural fibres connecting together the different parts 

 of the gray substance of the cerebrum, the cerebellum, and the deeper ganglia, and 

 finally the avenues of communication between the fibres of the encephalon and the cord, 

 are points of exceeding intricacy ; and many of them are still so uncertain and obscure, 

 that they cannot as yet be connected satisfactorily with the exact results of physiological 

 inquiry. All that we can do at present, is to recognize certain ganglionic masses, the 

 separate functions of which have been more or less accurately defined, and to show, as far 

 as possible, their anatomical relations to each other and to the spinal cord. 



The separate collections of gray matter concerning which we possess positive physio- 

 logical knowledge are, the gray matter of the cerebral hemispheres and of the cerebellum, 

 the corpora striata, optic thalami, tuber annulare, or pons, and the medulla oblongata. 

 To these may be added, the olfactory ganglia, which preside over the sense of smell, and 

 the tubercula quadrigemina, or optic lobes, which are the centres connected with vision. 

 The minute anatomy of the nerve-fibres and the nerve-cells, with their mode of connec- 

 tion with each other, have been already considered with sufficient minuteness under the 

 head of the general structure of the nervous system. We shall here discuss chiefly the 

 direction of the fibres through which the encephalic ganglia are connected with the periph- 

 ery, the fibres connecting the different ganglia with each -other, and, in the case of the 

 larger ganglia, certain commissural fibres connecting together their different parts. 



In the wealth of literature pertaining to the minute anatomy of the encephalon, it is 

 somewhat difficult to separate and define the well-established facts which have a direct 

 bearing upon physiology. Perhaps the most elaborate and, to a certain extent, the most 

 satisfactory observations upon the various points to be considered, are those of Luys ; but 

 this author describes the course of the fibres with an exactitude that seems hardly justi- 



