780 THE NERVOUS SYSTEM 



stance is composed of more or less definite bundles or fasciculi, each having a definite course, 

 and whose axones form links (conduction paths) in a definite system of neurone chains. 



Present information as to the size, position, and connections of the various fasciculi is based 

 upon evidence obtained by three different lines of investigation:— 



(1) Physiological investigation. — (a) Direct stimulation of definite bundles or areas in 

 section and carefully noting the resulting reactions which indicate the function and course of 

 the axones stimulated. (6) 'Wallerian degeneration' and the application of such methods as 

 that of Marchi. When an axone is severed, that portion of it which is separated from its parent 

 cell-body degenerates. Likewise a bundle of axones severed from their cells of origin, whether 

 by accident or design, will degenerate from the point of the lesion on to the locality of their 

 termination in whichever direction this may be. This phenomenon was noted by Waller in 

 1852 and is known as Wallerian degeneration. By the application of a staining technique 

 which is differential for degenerated or degenerating axones and a study of serial sections con- 

 taining the axones in question, their course and distribution may be determined. The locality 

 of their cells of origin, if unknown, may be determined by repeated experiment till a point of 

 lesion is found not followed by degeneration of the axones under investigation, (c) The axonic 

 reaction or 'reaction from a distance.' Cell-bodies whose axones have been severed undergo 

 chemical change and stain differently from those whose axones are intact. Thus cell-bodies 

 giving origin to a bundle of severed axones may.be located in correctly stained sections of the 

 region containing them. 



(2) Embryological evidence. — In the first stages of their development axones of the cere- 

 bro-spinal nervous system are non-medullated. They acquire their sheaths of myehn later. 

 Axone pathways forming different chains become medullated at different periods. Based 

 upon this fact a method of investigation originated by Flechsig is employed, by which the posi- 

 tion and course of various pathways may be determined. A staining method differential for 

 medullated axones alone is apphed to the nervous systems of foetuses of different ages, and path- 

 ways medullated at given stages may be followed from the locality of their origin to their 

 termination. In the later stages, when most of the pathways are medullated and therefore 

 stain alike, the less precocious pathways may be followed by their absence of meduUation. 



(3) Direct anatomical evidence.— (a) Stains differential for axones alone are applied to a 

 given locality to determine the fact that the axones of a given bundle actually arise from the 

 ceU-bodies there, or that axones traced to a given locality actually terminate about the cell- 

 bodies of that locality. For example, it may be proved anatomically that the axones of a dorsal 

 root arise from the cells of the corresponding spinal ganglion, and then these axones may be 

 traced into the spinal cord and their terminations noted either by collateral or terminal twigs, 

 or the fasciculus they join in their cephalic course may be determined, (b) The staining prop- 

 erties and the size and distribution of the tigroid masses in the ceU-bodies of sensory neurones 

 differ from those in the motor neurones, and recently Malone has claimed that, in the central 

 system, the cell-bodies in the nuclei of sensory neurone chains, those ascending toward the cere- 

 bral cortex, may be distinguished from the cell-bodies of the motor or descending chains by the 

 arrangement and size of their tigroid masses. He claims further that in the same way, the cell- 

 bodies of the somatic efferent neurones may be distinguished from those of the visceral 

 efferent neurones. In this way the locality of origin of certain physiologically known paths 

 may be determined. 



(4) The so-called pathologico-anatomical method is based upon the same general principles 

 as is the physiological (or experimental) method. A pathological lesion, a local infection or a 

 tumor for example, may destroy a nucleus of cell-bodies or sever a bundle of axones, and the 

 resulting degeneration of the axones may be followed through serial sections suitably prepared. 

 The locality of the lesion known, the path may be followed to determine the locality of its ter- 

 mination; its locality of termination known from the symptoms resulting, the path may be fol- 

 lowed to its cells of origin, or to determine whatever be the locality of the lesion. 



Funiculi. — In order that the various fasciculi may be referred to with 

 greater ease, the white substance of the spinal cord in section is divided into three 

 areas known as funiculi or columns and which correspond to the funiculi already 

 mentioned as evident upon the surface of the cord when intact. The funiculi are 

 outlined wholly upon the basis of their position in the cord and with reference to 

 the median line and the contour of the column of grey substance; their component 

 fasciculi are defined upon the basis of function. (1) The posterior funiculus or 

 column is bounded by the posterior median septum and the line of the dorsal horn; 

 (2) the lateral funiculus or column is bounded by the lateral concavity of the gre}^ 

 column and the lines of entrance and exit of the dorsal and ventral roots; (3) the 

 ventral funiculus or column is bounded by the line of exit of the ventral roots, 

 and by the anterior median fissure. 



The posterior funiculus or column [funiculus posterior]. — This funiculus is 

 composed of two general varieties of axones arranged in five fasciculi. First, and 

 constituting the predominant type in all the higher segments of the cord, arc the 

 afferent or general sensory axones, which arise in the spinal ganglia, enter the cord 

 by the dorsal roots, assume their distribution to the neurones of the cord, and then 

 take their ascending course toward the ence])halon. The axone of the spinal 

 ganglion neurone undergoes a T-sliaped division a short distance from the cell- 

 body, one limb of this division terminating in tin; i^eripheral organs and the other 

 going to form the dorsal root. Upon entering the cord the dorsal root axones 



