656 



NERVOUS SYSTEM. (NERVOUS CENTRES. THE SPINAL CORD.) 



fibrous substance, and that it is applied from 

 within outwards on the surface of this latter. 

 Consequently, the opinion of M. Gall, that it 

 is formed prior to the medullary, and is, as 

 it were, the matrix, is absolutely false with 

 regard to the spinal marrow, for we already 

 perceive the roots of the spinal nerves, in 

 the second and third months, although at this 

 period there is no cortical yet deposited in its 

 canal." 



" It is very remarkable that the canal of the 

 spinal marrow exists constantly and during the 

 entire life of the animal, in fishes, reptiles, and 

 birds. I have met it in a great number of 

 fishes, both of salt and fresh water, such as 

 the ray (Raiu), shark (Syualus), bream 

 ( Cyprinus bra?t/a), bandfish (Cepola), pike 

 ( Esox), salmon, carp, &c.; and I have always 

 found its internal surface covered with a layer 

 of grey substance. The observations of M. 

 Arsaky agree perfectly with mine in this re- 

 spect."* 



" I have observed the same canal, in ques- 

 tion, in the hawk's-bill tortoise, common tor- 

 toise, a young crocodile of the Nile, wall li- 

 zard, ringed snake, land salamander, green 

 frog, and the common toad. In front it is 

 continuous with the fourth ventricle, or rather 

 it dilates to give origin to this cavity, and its 

 interior was covered with a thin layer of cortical 

 substance." 



" Birds possess this canal both in their 

 embryo state and in adult age. In these it 

 forms, at its inferior part, a remarkable exca- 

 vation, which Steno, Perault, Jacoboeus, and 

 some other authors have described under the 

 name of the rhomboidal sinus. In birds, also, 

 the grey substance occupies the interior, and is 

 no where in greater abundance than on the 

 walls of this sinus." 



" The canal equally exists in the spinal mar- 

 row of the foetus of mammiferous animals, as 

 also in the young animals of this class (?) F. 

 Meckel has found it in the embryo of the rab- 

 bit ;f and G. Sewell in young animals of the 

 genus dog, sheep, ox, and horse. \ This latter 

 writer observes that it was filled with a colour- 

 less fluid, nearly opaque, and of the same na- 

 ture as that which existed in the ventricles. 

 F. Meckel has even met a small canal full of 

 fluid in the spinal marrow of some of the adult 

 mammiferous class, such as the dog, cat, rabbit, 

 sheep, and ox. Blaes has met it also in many 

 adult mammiferous animals. 



" Although we cannot find this canal in the 

 spinal marrow of the human adult in its nor- 

 mal state of developement, still it has undoubt- 

 edly been met with; we should, then, consider 

 it as the result of a retardation in its develope- 

 ment. Charles Stephen was the first who 

 gave a description of it; and Columbo,|| Pic- 



* Diss. de piscium cerebro et medulla spinali. 

 Halle, 1813, p. 9. 



t Beitrage zur Vergleichend : Anatomie, cap. ii. 

 No. i. p. 32. 



t Phil. Trans, for 1809. 



De dissectione partium corporis humani, lib. iii. 

 Par. 1545. 



|| De re anatomicu, Ven. 1559. 



colhomini,* Bauhin,f Malpighi,J Lyser, 

 Golles,|| Morgagni,1f Haller,** and M.Portal,tf 

 have since observed it. Many of these writers 

 have even considered it as a constant and nor- 

 mal disposition ; an hypothesis which Varoli, 

 Monro, Sabatier, and some other anatomists 

 have justly opposed. Nymman proceeded 

 even still further, for he spoke of two canals 

 prolonged into the spinal marrow. Gall pre- 

 tends to have found in the spinal marrow of 

 new-born infants, in infants of a certain age, 

 and even in certain adults, two canals free 

 from all communication with the fourth ven- 

 tricle, but which extended through the pons 

 Varolii,the tubercula quadrigemina and the me- 

 dulla oblongata into the interior of the optic tha- 

 lam i, where they formed a cavity sufficient to 

 lodge an almond ! These two supposed canals, 

 with their termination in the optic thalami, do 

 not exist ; we must suppose that they are pro- 

 duced by a forced insufflation : I have never 

 met them either in the adult or in the fcetus; 

 nor do we find them in animals in which the 

 canal of the spinal marrow always communi- 

 cates with the fourth ventricle, by means of 

 the calamus scriptorius."J| 



We shall notice further on the recent state- 

 ment of Stilling and Wallack on this subject. 



Bloodvessels of the spinal cord. The arteries 

 of the spinal cord are derived from the verte- 

 bral arteries as well as from the small vessels 

 which ramify upon the spinal column in the 

 cervical, dorsal, and lumbar regions. 



Of these the largest and most important are 

 the two spinal arteries which spring from the 

 vertebral on each side, distinguished as the 

 anterior and posterior spinal arteries. 



The anterior spinal artery is the larger of the 

 two. It arises from the vertebral artery near to 

 the basilar : sometimes it comes from the ba- 

 silar itself, or from the inferior cerebellar ; and 

 sometimes the arteries of opposite sides have 

 different origins, one arising from the vertebral 

 and the other from the basilar. It passes nearly 

 vertically downwards, inclining inwards, in front 

 of the medulla oblongata, and having passed 

 for a short distance in front of the cord, it 

 unites at an acute angle with its fellow of the 

 opposite side, forming a single vessel, which 

 passes down in front of the anterior median 

 fissure, under cover of the band of white fibrous 

 tissue which is found along the middle of the 

 anterior surface of the cord. The artery thus 

 formed is called the anterior median artery of 

 the spinal cord. 



" The anterior or median spinal artery," says 

 Cruveilhier, " therefore, results from the anas- 



* Anatom. Prslectiones, Rom. 1586. 



t Theatrum Anatomicura. Francf. 1605. 



t De cerebro, in his Opera Minora, t. ii. p. 119. 



Culter A&atomicns. Copenhag. 1653. 



|| Abrege de 1'ceconomie du grand et petit monde. 

 1670. 



1f Adversar. Anatom. Animadv. xiv. 

 ' Elem. Physiologic, t. iv. 



ft Observ. sur un spina bilida et sur le canal de 

 la mbelle epiniere : dans Mem. de 1'Acad. des Sc. 

 1770. 



II Dr. Bennett's translation of Tiedemann's Ana- 

 tomy of the Fcetal Brain, pp. 124 et sqq. 



