242 Dr. Bealc Croonian Lecture. [May 11, 



fibres. Indeed the observer often fails to trace an individual dark-bordered 

 fibre for any great distance in consequence of its becoming exceedingly fine 

 at the point where it crosses, or is crossed by other dark-bordered fibres. 

 Not only so, but where a bundle of comparatively wide dark-bordered fibres 

 passes through a small aperture, as for example in a bone, the fibres appear, 

 as it were, drawn out to exceedingly thin threads, as represented in this 

 figure. 



And it may be fairly argued that since a wide dark -bordered fibre may 

 be reduced in certain parts of its course to a fine cord not more than the 

 soocx^h f an i nc ^ m Diameter, without its integrity or conducting-powor 

 being interfered with, there is nothing unreasonable in concluding that fine 

 fibres of the same diameter are efficient conductors of the nerve-current, 

 although their length may be considerable. And I have shown that iu 

 many of the tissues of the frog (bladder, connective tissue, auricle, &c.), the 

 finest branches of the nerves at their distribution are invariably less than 

 the aoiootb f an inch in diameter. Is it then probable that the nerves 

 distributed to the elementary fibres of the voluntary muscles of the limbs 

 should form the single exception to this very general arrangement, and that 

 the peripheral nerves of muscle should exhibit the dark-bordered character 

 up to, or to within, a very short distance of their ultimate distribution or 

 termination, as is maintained by many German anatomists. 



Of the distribution of the pale nucleated nerve-fibres to the elementary 

 muscular fibres. 



Few anatomical questions have received of late years a larger share of at- 

 tention than the ultimate arrangement of nerve-fibres in voluntary muscle. 

 It is a matter of regret to me that although I have studied the question in 

 many ways during the last five years, my conclusions do not accord with 

 those of any other observer. And I must admit that although the German 

 writers differ from one another on not unimportant points, they, nevertheless, 

 agree in this, that the nerves form ends, pass into end-organs, or exhibit 

 terminal extremities of some kind ; while on the other hand my observations 

 have led me to conclude not only that nerves never terminate in ends in vo- 

 tary muscle, but that there are no terminal extremities or ends in any nervous 

 organ whatever. 



With regard to the ultimate arrangement of nerves in muscle, the con- 

 clusions of Kolliker accord more nearly with my own than those of any 

 other observer. (Compare Kolliker' s statements iu his Croonian Lecture 

 delivered in 1862, with the results stated in my paper, published in the 

 Phil. Trans, for 1860.) Kolliker agrees with me in the opinion that the 

 nerves lie upon the external surface of the sarcolemma ; but what he regards 

 as ends or natural terminations, I believe to be mere breaks or interruptions 

 in fibres which in their natural state were prolonged continuously. 



And there is this further broad difference between foreign observers and 

 myself, that while they consider that each elementary muscular fibre is very 



