66 APPENDIX. 



of the spinal marrow, and which, when they cease to be distinct, represent a vault co- 

 vering a large ventricle, whose successive contraction gives rise to the aqueductus 

 sylvii. 



" 4. The pyramidal cords of the spinal marrow, which take a direction below up- 

 ward, and from bekind forward, after having produced two swellings, or ganglia, the 

 optic thalami, and corpora striata, each terminate by a lamina, which bent from before 

 backward, and from the side towards the superior and internal part, forms the com- 

 mencement of the hemisphere of the brain. These membranes and thin hemispheres 

 are so small at the second month, that they scarcely cover the corpora striata. In pro- 

 portion -as they increase they extend backward, and cover, at the third month, the optic 

 thalami ; at the fourth, the tubercula quadrigemina ; and, at the sixth or seventh, the 

 cerebellum. The lateral ventricles result from their inversion. 



"5. The medullary fibres of the pyramidal cords, previously to the formation of the 

 tuber-annulare, are immediately continuous with those of the crura cerebri ; from 

 whence the eye may readily trace them in the optic thalami, and corpora striata, and see 

 them aftewards spreading and radiating in the hemispheres. 



" fl. The parietes of the hemispheres gradually increase in thickness in proportion as 

 new strata of cerebral substance are deposited on the surface ; and convolutions- are not 

 decidedly seen till towards the close of pregnancy. 



" All these combined facts clearly demonstrate, in the opinion of Dr. Tiedernann, that 

 the brain and cerebellum proceed from the spinal marrow : or that, to employ a mo- 

 dern expression, they are an efflorescence of it. In running through the scale of ani- 

 mals, ample confirmation may be found of the assertions here advanced. The structure 

 of the encephalon and spinal marrow becomes complicated in proportion as we ascend 

 from fishes to reptiles, birds and mammalia. If the contrary opinion were correct if 

 the spinal marrow were derived from the brain, the cerebrum and cerebellum must ne- 

 cessarily be found the first formed in the foetus, which is not the case. It is equally 

 necessary that, in the animal scale, where it is impossible to mistake a gradation in the 

 figure and developement of the organs, that a complete brain should exist previously to 

 any trace of a spinal marrow ; but this is never observed. Comparative anatomy, on 

 the contrary, shows that the spinal marrow is very large in the inferior classes of ani- 

 mals, while the brain forms but a small and delicate prolongation of it ; and in ascend- 

 ing from reptiles to birds and mammalia, it is seen gradually to increase in volume and 

 complication, as abs6lutely takes place in the foetal encephalon*. 



* Prochaska and the Wenzels conclude from their microscopic observations, that the 

 brain is composed of a number of small globules of a tolerably firm consistence con- 

 tained in a flocculent pulp. The researches of Mr. Bauer into the ultimate structure of 

 this organ are more precise. He considers that the brain and nerves consist of extemely 

 delicate fibres, formed of minute globules, connected together by a transparent gelan- 

 tinous fluid, or viscid mucus, which is soluble in water. These globules vary in dimen- 

 sions, from j-g Q- to -j-^Q-g- parts of an inch. " The principal difference," he states, " in 

 the appearance of the different parts of the brain, consists in the proportions which the 

 quantity of mucus and fluid bear to the quantity of globular tissue, and in some measure,, 

 in the size of the globules. The cortical substance of the cerebrum and cerebellum 

 is made up by the small globules, the gelantinous fluid and mucus being very abundant. 

 The medullary substance in the cerebrum and cerebellum differs from the above, in 

 the large globules prevailing, the mucus being more tenacious and less abundant. The 

 crura cerebri and cc rebelli resemble the medullary substance, only that the mucus and 

 fliu Is are more abundant, and in greater proportion than the globules. 



The medulla oblongata, the corpora pyramydalia, and olivam, have nearly the same 

 structure as the medullary substance, but the mucus is very abundant. In the medul- 

 la spinalis, the mucus and fluid are less tenacious, but in greater quantity than in any 

 part of the brain. 



Every part of the brain is pervaded by innumerable bloodtvessels, which are of consi- 

 derable size towards the centre, but branch out to an extreme degree of minuteness ; 

 but even then carry red blood. The arteries in the brain never anastomose, and are 

 accompanied by veins still smaller, which are supplied with valves. 



This view of the structure of the cerebrum and cerebellum is calculated, In the opi- 

 nion of Sir Everard Home, to throw considerable light on the functions of the brain. 

 He thinks that the cortical substance is one of the most essential parts of this organ, 

 and considers it the. seat of memory, from having observed that that faculty is destroyed 

 or materially diminished by any undue pressure upon the upper anterior part of the 





