88 ANATOMY FOR NUKSES. [CHAP. VII. 



or less continuous column, and as forming the core of the cen- 

 tral nervous system, while around it are built up the great 

 mass of the cerebrum and the smaller mass of the cerebellum. 

 This central core is connected by various bundles of fibres with 

 the spinal cord, besides being, as it were, a continuation of the 

 gray matter in the centre of the cord. It is also connected at 

 its upper end, by numberless fibres, to the gray matter on the 

 surface of the cerebrum. 



The average weight of the brain in the male is 49| oz. (1403 

 grammes) 1 ; in the female, 44 oz. (1247 grammes). It appears 

 that the weight of the brain increases rapidly up to the seventh 

 year, more slowly to between sixteen and twenty, and still more 

 slowly to between thirty and forty, when it reaches its maxi- 

 mum. Beyond this age the brain diminishes slowly in weight, 

 about an ounce every ten years. The size of the brain bears a 

 general relation to the capacity of the individual. Cuvier's 

 brain weighed rather more than 64 oz. (1814 grammes), while 

 the brain of an idiot seldom weighs more than 23 oz. (652 

 grammes). The number and depth of the cerebral convolu- 

 tions also bear a close relation to intellectual power ; babies and 

 idiots have few and shallow folds, while the brains of men of 

 intellect are always markedly convoluted. 



The cranial nerves. The cranial nerves, twelve in number on 

 each side, arise from the base of the brain and medulla oblon- 

 gata (vide Fig. 73), and pass out through openings in the base 

 of the skull. They are named numerically according to the 

 order in which they arise from the brain. Other names are 

 also given to them derived from the parts to which they are 

 distributed, or from their functions. Taken in their order 

 from before backwards, they are as follows : 



1. Olfactory (sensory). 



2. Optic (sensory). 



3. Oculomotor (motor). 



4. Pathetic or Trochlear (motor). 



5. Trifacial or Trigeminal (mixed). 



6. Abducens (motor). 



7. Facial (motor). 



8. Auditory (sensory). 



1 Avoirdupois weights are used in weighing the organs of the body. One oz. 

 avoirdupois = 28.35 grammes. 



