662 



NERVOUS SYSTEM. (NERVOUS CENTRES. THE ENCEPUALON.) 



mammalia.* This statement, although appli- 

 cable to the encephalic mass when viewed as a 

 whole, does not apply to certain of its parts, 

 which are often more developed in the less 

 perfect than in the more highly organized ani- 

 mals. The cerebrum and cerebellum, however, 

 exhibit this gradual increase of developement, 

 and their enlargement is in accordance with a 

 gradually increasing manifestation of mental fa- 

 culties. And it is upon the great size of these 

 parts that the superiority of the human brain 

 over that of all other animals depends. 



In comparing the brains of some of the 

 larger mammalia with that of man, we observe 

 an evident want of correspondence between 

 the bulk of the encephalic nerves and that of 

 the encephalon itself. This does not accord 

 with what we have had occasion to notice 

 respecting the spinal cord, in which large 

 nerves were always concomitant with high 

 developement of the organ itself. The maximum 

 weight, as Miiller remarks, of a horse's brain is, 

 according to Soemmering, 1 Ib. 7oz.; the mini- 

 mum of an adult human brain 2 Ib. 5^ oz.; and, 

 nevertheless, the nerves at the base of the brain 

 are ten times thicker in the horse than in the 

 human subject. 



This want of correspondence between the 

 developement of the mass of the body and that 

 of the brain, as well as between the size of that 

 organ and of the encephalic nerves, must surely 

 be admitted to indicate an incorrectness in the 

 assertion of the distinguished physiologist who 

 has just been quoted, namely, that " all the 

 primitive fibres of the nerves terminate in the 

 brain; those of the cerebral nerves immediately, 

 those of the spinal nerves through the medium 

 of the spinal cord."f The human brain must 

 evidently contain numerous other fibres besides 

 those which are continuous with the roots of 



the nerves, and it is likely that the horse's brain 

 contains similar ones, although less numerous ; 

 it seems, therefore, impossible that the small 

 brain of the horse can be the point of con- 

 vergence of the large spinal and cerebral nerves 

 of that animal ; and if this be true as regards 

 the horse, it is so likewise in man. It is much 

 more probable that a large proportion of them 

 do not extend beyond the spinal cord, and that 

 the greater number of the fibres of the ence- 

 phalic nerves do not go beyond the part in 

 which they are immediately implanted. 



It must be admitted, however, that although 

 this disproportion is very manifest as regards 

 the whole encephalon, it is not so evident when 

 we compare the nerves with those segments of 

 the organ from which they immediately arise. 

 Thus, the medulla oblongata is always, as 

 regards mere bulk, in the direct ratio of its 

 nerves ; the optic lobes a e large when the 

 optic nerves are so ; the olfactory lobes bear a 

 close relation to the number of the olfactory 

 nerves, and it may be added, to the complication 

 of the olfactory organ. It is to the cerebral 

 hemispheres, to the cerebellum and the systems 

 of fibres immediately connected with them that 

 we must attribute the disproportion in question : 

 those parts being small when the nerves are 

 large, as in the horse, and large when the nerves 

 are of small size, as in man. 



The human encephalon weighs about 48 oz. 

 for the male, and 44 oz. for the female.* This 

 estimate, which was formed by Krause, does 

 not differ very materially from that derived 

 from Professor John Reid's careful observa- 

 tions made at the Royal Infirmary at Edin- 

 burgh. The following tables are extracted 

 from a paper by this excellent anatomist in the 

 London and Edinburgh Monthly Journal of 

 Medical Science for April, 1843.f 



TABLE I. 



Average weight of the encephalon, &c. between 25 and 55 years of age, in the two sexes, 

 and the average difference between them Males, 53 brains weighed Females, 34 brains 

 weighed : Difference in 



Cerebrum 



Cerebellum 



Cerebellum, with pons & medulla oblonga 



TABLE II. 



Relative weight of encephalon to cerebellum, and to cerebellum with medulla oblongata and 

 pons Varolii, between 25 and 55 years of age, in the two sexes (53 male and 34 female 

 brains weighed). Male- Female 



Relative weight of encephalon to cerebellum as 1 to 9^ as 1 to 9] 



Ditto to ditto, with pons and medulla oblongata 1 8-& 1 7 T 9 5 



From this table it would appear that, in the 

 female, the average cerebellum is, relative to the 

 encephalon, a little heavier than in the male. 



In a third table, which has been reduced 

 from that published by Professor Reid, the 

 average weight of the encephalon, cerebellum, 

 with pons Varolii and medulla oblongata, is 

 given over a much wider range of age than that 



* See the table at p. 623 of this volume. 

 t Physiol. trans), by Baly, 2nd ed. p. 796. 



in the first table quoted. For this purpose 



253 brains were weighed. 



* According to Mr. Hamilton's investigations, 

 the adult male brain in the Scot's head weighs, on 

 an average, 3 Ibs. 8 oz. troy ; about one brain of 

 seven is found about 4 Ibs. troy; the female brain 

 weighs 3 Ibs. 4 oz. ; and one of a hundred female 

 brains weighs 4 Ibs. 



t Reference may also be made to an extensive 

 series of observations on the weight of the brain 

 by Dr. Sims, Med. Chir. Trans, vol. xix. p. 353. 



