NERVES. 467 



larger tubes, collected into bundles. These tubes are the immediate prolong- 

 ations of the jointed tubes of the brain and spinal chord, for the most part 

 suddenly changed and deprived of their dilatations, and are surrounded by 

 neurilema. In the invertebrata they are from ^ to ^ of a line in diameter : 

 in the vertebrata from T | to 5^. They contain a granular, and, as it were, 

 congealed, medullary matter, that by gentle pressure can visibly be forced out 

 from them, after which they appear as empty sheaths, &c. niwr -t 



7. Hence the nervous substance consists of jointed tubes carrying the 

 liquor nerveus, and cylindrical tubes with true nervous pith. 



8. The brain does not consist of nervous pith. 



9. The invertebrata do not possess a spinal chord consisting of jointed 

 tubes without pith ; or, in other words, the invertebrata have no spinal chord, 

 although their abdominal ganglionic chord, which consists chiefly of cylindrical 

 tubes containing pith, may perform the function of a spinal chord. 



10. In the invertebrata the jointed cerebral substance and blood globules 

 appear in much less proportion. 



11. The jointed nervous tubes are, in relation to the human organisation 

 and their distribution in the animal kingdom, the more important and noble part 

 of the nervous system, and more immediately subservient to sensation. 



12. Almost all cerebral terminations (only less obviously in the ear) are 

 pervaded by a network of vessels, and contain large scattered globules, the size 

 of which has a constant ratio to that of the blood globules in the same animal. 



13. The structure of the retina, even in man, has been hitherto very erro- 

 neously described. The granular layer of the anterior surface of the retina is 

 pervaded by a network derived from the central vessels. Behind this is placed 

 the expansion of the optic nerve, which consists of jointed tubes, and separates 

 into a peripheral cortical, and a central medullary matter. Many single, scat- 

 tered, club-shaped bodies appear to moderate the luminous impression. Their 

 connection with the jointed tubes of the nerve, Professor Ehrenberg could not 

 clearly make out. 



He confirms the discoveries of old anatomists mentioned above at page 341, 

 respecting the pulpy (cortical) substance, that it consists of a thick but delicate 

 vascular network, and a soft substance ; and the latter he pronounces to be 

 finely granular, and to contain numerous insulated larger granules, which are 

 composed of smaller ones, strung on filaments, as far as it was possible to observe 

 them. Near the fibrous (medullary) portion of the brain, the filaments of the 

 pulpy (cortical) substance become more and more evident, and the blood 

 vessels somewhat larger and much less numerous. These observations greatly 

 strengthen Gall's opinion of the pulpy (cortical) substance being the source of 

 the fibrous (medullary) : and Ehrenberg farther states, we see (12), that al- 

 most all the terminations of the cerebral nerves are again contained in a dense 

 vascular network, with scattered globules, which he conjectures to be the nuclei 

 of blood globules, especially as these in the pulpy substance of the brain are pro- 

 portionate to the size of the blood globules of the animal. 



Gall, it must be remembered, conceives that the nervous fibres originate, not 

 only in the pulpy portion of the encephalon and chord, but in the peripheral 

 extremities, where also pulpy substance, he urges, is found. In the pulpy 

 portion of the ganglia, similar granules have been discovered by Ehrenberg, so 



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