99 



HUMAN ANATOMY. 



I-u,. 837. 



Semidiagrammatic representation of 

 strut/line iii neurone; a, axone. 



On reaching their destination the- axones terminate in end-arborizations ( telodendria) 



of various forms, in a manner similar to tin- dendrites. According to the distribution 



of their axones, the neurones are divided into two 

 In those of the first, known as ee//s of type /, 

 th<- axone is continued as a nerve-fibre and is, therefore, 

 relatively 'oni;. Soon after leaving the cell-body such 

 axones -iv ot'f delicate lateral processes, the collaterals, 

 which, alter a longer or shorter course, break up into 

 arborizations ending in relation with other and often 

 remote neurones. Neurones of the second and much 

 less frequent cla->s, cells of type If, possess short axones 

 that are not continued as iierve-tibres, but almost 

 immediately break up into complex end-arborizations 

 or neuropodia ( Kollikcr >, limited to the gray matter. 

 The processes of the sensory neurones, as in the 

 case of those constituting the spinal and other ganglia 

 connected with afferent Derves, are so modified during 

 development (Fig. 839) that later both dendrites and 

 axones arise in common from the Dingle robust stalk of 

 an apparently unipolar cell. Branching T-like, one 

 process (the dendrite) passes towards the periphery 

 and the other (the axone) extends to and into the 

 cerebro-spinal axis. 



The nerve-cells, as the bodies of the neurones 

 are called, possess certain structural details in common, 

 although in some instances they present characteristics 



that suffice to identify them as In-longing to particular localities. Nerve-cells are 



relatively large elements, those in the anterior horns of the spinal cord measuring 



from .070-. 150 mm. in diameter, and contain a large spherical nucleus, poor in 



chromatin but usually pro- 



vided \\ith a conspicuous FIG. 838. 



niuleolus. Their cytoplasm 



varies in appearance with 



the method of fixation and 



staining to such an extent 



that considerable uncertain- 

 kfl to the relation 



of many described detaiU to 



the actual structure of the 



cells. It may be accepted 

 as established, ho\\rvrr, 

 that tile cell body of the 

 IK uroneconsjv ,, m i 



substance, homogeneou 



finely uranular, in which 



delicate jibrill<,- and m.. 



of ckromaiopkilit granules 



an embedded ; in addition, 

 a variable amount ot brown 

 or blackish pigment is coin 

 monly present in the vicin- 

 itv of the nucleus. The 

 n.e , ,f the tilnill.e 

 within the ner\e -cell, '. 



maintained 1,\ M,i\ 

 c I,,,],,. I,,,, 1,, ,. i; , 



garded, has been plai ed 



nd (pit -stion liy t! :! and ..th.Ts. The signifi- 



ami relations of the tibrill.r to the nei \ e -< ell. however, ha- ^i\ en rise to warm 



( human spinal cord stained to show Nll bodlet ; ^. 

 A, axones; < . tmpbnil 



400. 



