238 Dr. Beale Croonian Lecture. [May 11, 



of the frog : they are to be detected upon the iliac arteries in considerable 

 number. The results of Mr. Lister's experiments render it probable that 

 ganglia exist in connexion with the arteries of the limbs (Phil. Trans, 

 pt. 2 for 1858, p. 620). 



In this figure a small ganglion in course of development upon one of the 

 iliac arteries of the frog is represented ; and several fine branches of nerve- 

 fibres can be followed amongst the muscular fibre-cells. I have seen very 

 fine nerve-fibres beneath the circular muscular fibre-cells, apparently 

 lying just external to the lining membrane of the artery, and composed of 

 longitudinal fibjes with elongated nuclei an observation which confirms a 

 statement of Luschka's. I have not succeeded in satisfying myself that 

 nerve-fibres are ever distributed to the lining membrane of an artery, al- 

 though, from the appearances I have observed, I cannot assert that this is 

 not the case. In the auricle of the heart and at the commencement of the 

 venae cavae, very fine nerve-fibres are certainly distributed very near indeed 

 to the internal surface, being separated from the blood only by a very thin 

 layer of transparent tissue (connective tissue). 



The distribution of nerve-fibres to the coats of a small artery about the 

 g-jLjj-th of an inch in diameter is represented in this drawing. In all cases 

 (and I have examined vessels in almost all the tissues of the frog), not only 

 are nerve-fibres distributed in considerable number upon the external surface 

 of the artery, ramifying in the connective tissue, but I have also followed 

 the fibres amongst the circular fibres of the arterial coat. The nerves can 

 be as readily followed in the external coat as in the fibrous tissues generally ; 

 and the appearance of the finest nucleated nerve-fibres, already alluded to, 

 enables one to distinguish them most positively from the fibres of the con- 

 nective tissue in which they ramify. 



These nerves invariably form networks with wide meshes. I have de- 

 monstrated such an arrangement over and over again. A similar dispo- 

 sition may be seen in the auricle of the frog, 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 dis- 

 tinct terminations to the nerves distributed to the vessels of muscles. 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 demonstrate 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 there are no true 

 dark-bordered nerve-fibres, but we now know that the active part of a nerve 



