DISTKIBUTION OF NERVES TO ARTERIES OF THE FROG. 301 



the common frog, tyla, newt, toad, and in the snake, 

 slowworm, tortoise, and other reptilia. 



I have given a drawing in PI. XYI of a small gang- 

 lion in course of development removed from one of 

 the iliac arteries of the frog. Several fine branches of 

 nerve-fibres can be followed amongst the mnscular 

 fibre-cells of the artery in the same preparation. 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 fibres 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 

 the artery, although, 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 venag cav£e, very fine nerve-fibres unquestion- 

 ablv ramify 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 arteiy about the -g-^th part of an inch in 

 diameter is represented in fig. 2, PI. Y, p. 216, and to 

 somewhat larger vessels in fig. 4, PL XVI, and in the fig. 

 in PI. XVII, p. 303. 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 amonofst the circular fibres of the arterial coat. 

 The nerves can be as readily followed in the external 

 coat as in connective tissue generally ; and the 

 appearance of the finest nucleated nerve-fibres, 

 alreadv alluded to, enables one to distino-viish them 

 most positively fi'om the fibres of the connectiv 

 tissue in which they ramify. 



These nerves invariably form networks with wide 



