l86 Journal of Comparative Neurology. 



this manner, the nerve fibers are blue, muscle and nuclei, red. 

 The shape and structure of the ultimate nerve endings and their 

 relation to the heart muscle cell may, it seems to us, be more 

 clearly made out in preparations thus prepared, than in methy- 

 lene blue stained tissues fixed in ammonium picrate, or in pre- 

 parations stained after the chrome-silver method. 



Our results were briefly as follows : 



In sections of cat's auricle from lo to 20 ^ in thickness pre- 

 pared as above stated, portions of the intramuscular plexus, or 

 pericellular plexus, described by authors are abundantly seen. 

 The nerve fibers of this plexus are, as far as we have determined, 

 non-medullated. They vary, however, much in size, and in the 

 size and number of the varicose enlargements seen on them. They 

 often show relatively large sheath nuclei, clearly seen with these 

 stains; these nuclei stain red, the axis cylinder blue. The strands 

 of the intra-muscular plexus may consist of single fibers or small 

 bundles of fibers. We have now and then been able to trace 

 such a small bundle to some one of the sympathetic ganglia 

 situated in the wall of the auricle. Some of the non-medull- 

 ated fibers of the intra-muscular plexus are therefore, no doubt, 

 the neuraxes of sympathetic cells situated in the auricular wall. 

 Whether they all are, or what particular intra- muscular fibers 

 are, is a subject concerning which further research is needed. 

 From this intra-muscular plexus, one may now and then trace 

 a nerve fibril to its ending on a heart muscle cell. Such fibrils 

 are usually very varicose and terminate in endings which vary 

 in complexity. In Figs. 15 to 20, several such endings are re- 

 produced. They may be very simple, consisting of a small 

 terminal bulb, as shown in Fig. 15 ; these, it may be stated, 

 are most numerous ; or again, the fibril may branch just before 

 it terminates, into two short filaments, each of which ends in 

 small bulbar enlargements, as seen in Fig. 16. The endings 

 may however be much more complex, the nerve fiber termin- 

 ating in 4 to 8 small filaments, and ending in a terminal enlarge- 

 ment, as is shown in Figs. 17 to 20. The terminal end-bulbs 

 in these more complex endings are usually grouped in more or 

 less compact clusters as a majority of the figures show ; they 



