236 Dr. Beale Croonian Lecture. [May 11, 



The bundles of dark-bordered fibres which may be traced to the pos- 

 terior part of the frog's bladder divide and subdivide freely, spreading out 

 in the form of a lax network, the fibres constituting which may be followed 

 for some distance, and many may be traced to their ultimate distribution 

 in the thin tissue of the bladder. Over a great part of the frog's bladder, 

 however, no dark-bordered fibres or bundles of moderately coarse fibres 

 can be detected ; yet the organ is in every part very freely supplied with 

 nerves. 



Bundles of excessively fine fibres, first described by me*, may be traced 

 running parallel with many of the small arteries, and may be seen to divide 

 and subdivide into finer bundles, which at length form a plexiform net- 

 work. Here and there is seen a plexus of very fine fibres, from which 

 bundles of fine fibres diverge in different directions. That very many of 

 these fine fibres come from the numerous ganglion-cells found in connexion 

 with the nerve-trunks there is no doubt ; and it is equally certain that many 

 also result from the division and subdivision of dark -bordered fibres. But 

 whether the large dark-bordered fibres seen in the nerve-trunks pass directly 

 to their distribution in the bladder, or in the first place become connected 

 with ganglion- cells, it is difficult to decide with absolute certainty ; I have, 

 however, traced several of the large fibres directly from the trunks to their 

 distribution, but even in these instances I am not prepared to assert that no 

 branches pass to the ganglion-cells. My impression is that sometimes this 

 is the case, but that some of the fibres pass to their distribution without 

 there being any such connexion with ganglion- cells ; and I think it probable 

 that, of the fibres resulting from the division of a dark-bordered fibre derived 

 from the cord, some may become connected with ganglion-cells, while others 

 may pass to their distribution in the bladder without being connected with 

 these cells. 



In the very thin membrane of which the walls of the frog's bladder are 

 composed we may follow out the distribution of nerves a to the muscular 

 tissue, b to the surface of the mucous membrane, c to the vessels, and d to 

 the connective tissue. 



In this drawing the general arrangement of the nerve network is repre- 

 sented, from which fibres pass to supply all the tissues of the bladder. 



Upon the external surface of the lung of the frog muscular fibre-cells 

 exist in small number, and to these a network of delicate nerve-fibres is dis- 

 tributed. These muscular and nerve-fibres are, however, much more 

 highly developed upon the newt's lung than upon that of the frog. But 

 in this Lecture I restrict myself to the consideration of the distribution of 

 nerves to the muscular fibre-cells, which is described in very few words 

 and will be at once understood by reference to the diagram to which I now 

 direct attention. 



The muscular fibre-cells of the bladder itself and of the small arteries 



* " On very fine Nerve-fibres in Fibrous Tissues, and on Trunks composed of very 

 fine Fibres alone" (Archives of Medicine, vol. iv.). 



