SECT. II.] CONSTITUTION OF THE NERVOUS SYSTEM. 385 



cortical substance, the ventricles, together with the calamus 

 scriptorius, the plexus choroides, commissures, &c., are more 

 constantly present, and from this Haller concludes that these 

 divisions are the most essential.^ The brain is of the simplest 

 form in insects, in which there is little medullary matter, except 

 at the origin of the optic nerves;^ in some, it is bifid ; in others, 

 semibifid ; and, in others, only a nodule, called a brain, little 

 different from the nodules of the spinal cord.^ When it is of 

 this great degree of simplicity, it follows, that in the lowest 

 class of insects it is altogether wanting, and these also have no 

 eyes, according to Haller, nor does he think that in any 

 animal, eyes are unaccompanied by brain, or brain by eyes. 



It is manifest from these observations, that nature proceeds 

 gradually from the most perfect and highly complex brain to 

 the simpler and the simplest ; and that at last animals exist 

 altogether devoid of brain ; but what variety is there in the 

 nerves of various animals? or whether in all animals their 

 structure, number of fibrils, plexuses, and ganglia are the same 

 as in man? or whether (as it is probable) they become more 

 simple ? We have not as yet collected sufiicient observations 

 to answer these questions. What proportion the brain bears 

 to other parts of the body has been attempted to be shown by 

 observations and experiments, but what proportion the nerves 

 bear, as well to the brain, as to those parts not nerves, remains 

 unsolved. It was a conjecture only of Boerhaave and other 

 distinguished men, who taught that the brain in the foetus is 

 larger in proportion to the rest of the body than in the adult, 

 and that this is the case also as respects the nerves, of which 

 they believed the whole foetus, at its first formation, to consist, 

 so that the bones, cartilages, ligaments, muscles, tendons, and 

 all the viscera at their origin were merely nerves. Haller 

 scouted this doctrine,* while many distinguished men adopted 

 it too much, and he observes : " Nor do the nerves constitute 

 the common material from which nature fabricates the other 



' Oper. Min., torn, iii, p. 214. 



^ Haller, de Part. Corp. Hum. Fabr., torn, viii, p. 3. 



3 Ibid., p. 6. 



* El. Phys.,tom. iv, p. 271. Marherr also rejected the opinion in his * Praelect. ad 

 Boerhaavii Instit.,' torn, iii, pp. 9 — 11, &c. ; and A. Murray, in his * Diss, de Sensibi- 

 litate Ossium morbosa.' Upsalae, 1780. 



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