

ZOOLOGY FOR MEDICAL STUDENTS 



CHAP. 



manner up and down the spinal cord. From the longitudinal portion of 

 tin- fibre cross-pieces (collateral fibres Fig. 137, col) pass off at intervals, 

 which divide up into fine branches in intimate relation with a motor 

 J ion-cell. The question whether there is actual continuity of 

 un -e between the terminal twigs of the collateral and the cytoplasm 

 of the motor-cell or merely intimate contact is a particular case of one of 

 tin; most disputed problems regarding the structure of the vertebrate 

 body. While the obvious evidence in the way of observed fact has up 

 to the present failed to give a clear demonstration of such continuity 

 there is still a minority of investigators,, including the present writer, 



col. 



s.c. 



/// 



FIG. 137. 



a -iK.winK tin- relations <.t a spinal nerve to the spinal cord, col, Collateral branch of 



M root; </>, epidermis; M, motor ganglion - cell ; tn, nmsdc - librc ; 



tn.f, motor-fibre ; S, MOSOry ganglion-eel] ; s.c, spinal cord ; s.f, sensory fibre s.e spinal ganglion 



il loot. 



who regard such continuity as probably existing though it may be almost 



ible to demonstrate. 



The arrangement of ganglion-cells and nerve-fibres just described is 



"I |>hy>iol<)Mical interest inasmuch as it affords us a glimpse of the type 



of nervous ineclinnisni concerned in the production of reflex movements 



involuntary and immediate responses in the form of movement 



ry stimuli. A glance at the diagram will show how 



from the skin may readily influence the motor-cell 



"' ''" collateral and so arouse it to its particular form of 



"v. that of sending out a motor impulse to bring about contraction 



of the musi le fibre. 



