302 PISTRIBUT10N OF NERVES TO ARTERIES OF THE FROG. 



meshes. I have demonstrated such an arrangement 

 over and over again. A similar disposition may be 

 seen in the auricle of the frog's heart, in the coats of 

 the venae cavae near their origin from the auricle, 

 among the striped muscular fibres of the lymphatic 

 hearts of the posterior extremities of the frog, and in 

 other situations. Kolliker confesses that he has not 

 succeeded in observing distinct terminations to the 

 nerves distributed to the vessels. He states that 

 some arteries are completely destitute of nerves, and, 

 apparently without having given much attention to 

 the subject, says " hence it is evident that the walls 

 of the arteries are not in such essential need of nerves 

 as is usually supposed." It is easy to demonstrate 

 nerves in considerable number on all the arteries of 

 the frog, and in the case of certain vessels of man and 

 the higher animals in which we have failed to demon- 

 strate nerves, it is more reasonable to assume that 

 they are there, although they have not been seen, 

 than to infer their absence simply because we have 

 failed to render them distinct. In the case of the 

 umbilical arteries of the foetus and their subdivisions 

 in the placenta, it is quite certain that there are no 

 true dark-bordered nerve-fibres, but we now know 

 that the active part of a nerve may consist of an 

 exceedingly delicate, pale, and scarcely visible fibre, 

 connected with a nucleus. Such delicate fibres and 

 nuclei are to be demonstrated amongst the muscular 

 fibres of these arteries, but in consequence of not 

 having been able to trace them continuously for any 

 great distance, I cannot assert that they are true 

 nerves. No one, however, has yet proved that they 

 are not nerves, or has demonstrated their real nature. 

 The nerves which supply the small arterial 

 branches in the voluntary muscles of the frog, come 

 from the very same fibres which give off branches to 

 the muscles. I have seen a dark-bordered fibre 

 divide into two branches, one of which ramified upon 



