660 



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



tion of the pia mater with the nervous fibres 

 themselves. He also very properly cautions 

 the dissector against a deceptive appearance 

 connected with the passage of those blood- 

 vessels which enter the lateral fissure, in 

 order to reach the internal grey substance. 

 " Without due precaution," he adds, " these 

 vascular branches may themselves be readily 

 mistaken for nervous fibrils ; but they are es- 

 pecially liable to be productive of error, be- 

 cause, when they are made tense, they cause 

 those portions of the longitudinal fibres of the 

 cord, which are left between them to assume 

 exactly the appearance of flat transverse fibres ; 

 this circumstance probably misled Gall, and 

 induced him to suppose that all the fibres of 

 the spinal nerves were connected with the grey 

 substance." 



The following is Mr. Grainger's account of 

 the result of his examinations conducted with 

 the precautions above specified. 



" After repeated examinations, I satisfied 

 myself that each root was connected both with 

 the external fibrous part of the cord and the 

 internal grey substance. The following is what 

 appears to be the structure : after the two 

 roots have perforated the theca vertebralis, and 

 so reached the surface of the cord, it is well 

 known that their fibres begin to separate from 

 each other; of these fibres, some are lost in 

 the white substance, whilst others, entering 

 more deeply into the lateral furrows, are found 

 to continue their course, nearly at a right angle 

 with the spinal cord itself, as far as the grey 

 substance in which they are lost. But this ar- 

 rangement has no resemblance to the distinct 

 division into fasciculi, depicted by Mr. Mayo; 

 on the contrary, it is with great care only that 

 small, delicate, individual threads or striae, as 

 it were, are traced, dipping into the lateral 

 fissure, and at length joining the grey matter. 

 This difficulty is owing to the fact that whilst 

 the fibres on the outer surface of the pia mater 

 adhere very intimately with that strong mem- 

 brane, on its inner surface, the membrane be- 

 comes so extremely delicate, that the fibres 

 lose much of their firmness, and break on the 

 application of the least force ; an accident 

 which always happens if the pia mater be raised 

 from the surface of the spinal cord, beyond the 

 point where the nerves are attached. When 

 the filaments have penetrated into the fissure, 

 they lose their rounded figure and become flat- 

 tened, and are then seen passing to the grey 

 substance at a right angle to the longitudinal 

 fibres. It is extremely difficult, owing to the 

 delicacy of the parts, to determine the exact 

 relations which exist between the above fila- 

 ments and the grey matter ; but in a few dis- 

 sections I have been able to perceive these 

 fibrils running like delicate striae in the grey 

 substance. In one instance the fibres, being 

 more distinct than usual, an appearance was 

 presented having a remarkable resemblance to 

 that which is seen on making a section of the 

 corpus striatum in a recent brain, after the 

 method of Spurzheim. My friend and col- 

 league, Mr. Cooper, in this case counted dis- 

 tinctly five separate fibrils passing from the 



anterior root of one nerve, and there were some 

 other fibres derived from the same root, which 

 were not so plainly seen." 



" From numerous examinations," continues 

 Mr. Grainger, " I am induced to believe that 

 whenever the white fibres of the nervous system 

 become connected with the grey substance, 

 whether in the different masses of the brain, in 

 the spinal cord, or in the ganglions, the ar- 

 rangement is similar to what is seen in the 

 section of the corpus striatum to which refer- 

 ence has just been made. The fibres become as 

 it were encrusted with the grey matter, a dispo- 

 sition which may even be seen by a careful in- 

 spection in the convolutions of the cerebrum, 

 in which the radiating fibres of the crus ce- 

 rebri are observed like delicate striae." 



I have repeated the dissections of the roots 

 of the nerves in the manner described by 

 Mr. Grainger, and am enabled to confirm his 

 general results. It appeared to me, however, 

 that considerably the greater number of the 

 fibres passed in at right angles, whilst those 

 which might be supposed to take an upward 

 course were few and indistinct, and seemed 

 rather to pass obliquely inwards and slightly 

 upwards than to approach the vertical direction. 

 In short, when the fibres had penetrated the 

 medullary substance, they seemed to diverge 

 from one another, those which occupied a 

 central position preserving much more of paral- 

 lelism than either the upper or the lower ones. 

 It is extremely difficult to demonstrate the 

 direct continuity between the fibres of the 

 nervous roots and those of the cord. Valentin 

 has, indeed, depicted the transition of nerve 

 fibres into the spinal cord (see^/zg. 330, p. 592) 

 as seen by the microscope; but these may be 

 passing to the grey matter of the cord. The 

 continuity of the fibres of the nerves with the 

 longitudinal fibres of the cord would probably 

 take place at the surface of the latter in greater 

 numbers than at more deeply-seated planes. 

 In the dissections above described, such fibres 

 would be very apt to be destroyed or to be 

 overlooked. Mr. Grainger, in the work before 

 referred to, speaks evidently with much greater 

 confidence of the connexion of the roots of the 

 nerves with the grey matter than of their con- 

 tinuity with the longitudinal fibres. He ex- 

 presses his conviction, however, that such a 

 continuity does exist, although the exact mode 

 of connexion and the situation at which it 

 occurs cannot be demonstrated. 



This question, respecting the precise relation 

 of the roots of the nerves to the cord, is one of 

 those in which physiology in a certain sense 

 takes the lead of anatomy. Experiment has 

 made it certain that while the spinal cord serves 

 as a propagator of nervous power to and from 

 the brain, as in the ordinary sensations and 

 voluntary movements of the trunk and extremi- 

 ties, it is likewise capable of acting as an 

 independent nervous centre, and that move- 

 ments of a very definite character may be pro- 

 duced in parts connected with it, even after all 

 communication between it and the brain has 

 been cut off. And it has been supposed by 

 one of the most zealous labourers in this depart- 



