68 APPENDIX. 



In another part of these notes we gave a full detail of the progressive development of 

 the cerebro-spim-1 system of nerves in the human ftctus. It will readily appear from 

 what we there advanced, that a similar gradation, (from the simplest to the most com- 

 plicated and perfect state of the Y,-; -. vous structure,) to that which we observe in ascend- 

 ing the scale of the animal creation, may L-e remarked in the changes which the nervous 

 system undergoes in the progressive evolution of the human embryo. In the lowest 

 of all the animal kingdom the nervous matter is not organized in a manner distinct 

 from the tissue constituting the anim?l : the nervous globules are disseminated through 

 an amorphous and pulpy mass. As we ascend the scale we perceive this particular struc- 

 ture arranged in succession into ganglia ; then into ganglia and spinal marrow ; and lastly 

 into ganglia, a spinal marrow and a brain, each becoming more perfect as we ascend the 

 scale, and the gradation from the one to the other being nearly unappreciable in the 

 species or genera, but sufficiently remarkable in the orders. A development of the 

 nervous system, in which a similar progression to this is observed, takes place in the 

 formation of the human fa-tus, and in that of the most perfect animals ; and a similar 

 type to that, in which this system exists in the lower orders, is adopted at first in the 

 highest, and preserved, every successive state of organization which this system as- 

 sumes in its progressive development being additions to that previously adopted, whilst 

 in the process of formation as respects the entire animal, each intermediate series from 

 the lowest, which is its first state of existence in the embyro, is successively passed 

 through, until the foetus arrives at that specific condition and stage of organization be- 

 stowed on the species to which it belongs. Thus the human foetus in the progress of 

 its formation, as respects both its nervous system and other organs and textures, runs 

 through the different grades of organization from the lowest, to that of the head of which 

 it is itself placed, j- ( See the Note on the Development of the Fatus. ) 



II. Of the Functions of distinct parts of the Cerebro-Spinal Order of the J\ervous Sys- 

 tem The researches of M. Flourens into the functions of the cerebro-spinal order of 

 nerves, have lately added greatly to our knowledge as to actions in which distinct parts 

 of this part of the nervous system are more particularly concerned. But before we 

 can give any account of the conclusions at which he has arrived, we must briefly no- 

 tice the meaning lie has attached to some of the terms which he employs. 



The term contractibility he very properly limits to the property inherent in the mus- 

 cular fibre only, of undergoing brisk contractions under the application of stimuli : and. 

 the term sensibility, to imply the property of experiencing sensations. The word irri- 



f Sir Everard Home, Merrs. GeofFroy Saint Hilaire and Blainville and Dr. Schultze, 

 consider that the skeleton of animals was intended more to prevent the nervous and 

 vascular system from being compressed or suffering any other injury, than to give form 

 and the power of motion to the body. The last named physiologist (Jlllgemeine En- 

 tyclopccdiefur Practische Jlrx'.e und Wundarzte, 1 theil, 1 band Ltip. 1 820.) concludes : 



1 " That the spinal marrow and vertebral column at all times exist together, even 

 only the slightest vestiges of the osseous system can yet be found. 



2 " That the osseous and nervous systems have between them numerous intimate 

 relations, both physiological and pathological. 



3 " That the more the exterior hard envelopment penetrates the interior of the bo- 

 dy, and approaches towards the nervous system, the more also are the phenomena of 

 sensibility developed, and nice vtrsa. 



4. " That the organs possess more or less importance according as they are more or 

 less protected from external influence by bones." 



The blood proceeding from the mass of muscles, spine and spinal marrow, is empti- 

 ed into the great spinal veins, as into a reservoir ; when it passes into the veins placed 

 on the sides and anterior surface of the spine, and thence into the superior und inferior 

 cavs:. 



By what power, it has been asked, is the blood which arrives in the two great spinal 

 veins, driven from them ? These veins may effect the propulsion of the blood which 

 they contain, by the vital properties with which they are endowed ; the blood may be 

 drawn oui of them, owing to their proximity to the cava by the dilatation of the cavities 

 of the heart : or by both influences combined. 



