98 Journal of Comparative Neurology. 



entrance into the myocardium to form a fundamental myocar- 

 dial plexus from which the system of intermuscular fibers orig- 

 inates. It is from the latter that the terminal fibers arise which 

 penetrate between the cells of the muscle bundles and enter into 

 communication with them by the medium of lateral and termi- 

 nal branches of varied form and size, comparable for the most 

 part to the terminations described in striped muscle of different 

 invertebrates." 



My own observations on the innervation of cardiac muscle, 

 were made largely on the auricle of the cat's heart. The tissue 

 was stained in methylen-blue, fixed in ammonia molybdate, sec- 

 tioned and counter-stained in alum carmine. In such prepara- 

 tions, the plexus of non-medullated fibers around the bundles 

 of heart muscle cells, described by other investigators, may 

 easily be seen. In the auricular wall, numerous small ganglia, 

 composed of sympathetic cells, are found. From such ganglia 

 one may often trace small bundles, made up largely of non- 

 medullated fibers (no doubt the neuraxes of the sympathetic 

 neurons constituting the ganglia, although, owing to the fact 

 that as a rule the cell bodies of the neurons are not stained with 

 the methylen-blue, the tracing of the neuraxes to their respect- 

 ive nerve cells often becomes a matter of extreme difficulty) 

 into the above mentioned plexus. 



From such plexuses, single varicose fibers, or small bun- 

 dles composed of two, three or four such fibers, can be traced 

 between the heart muscle cells and can often be followed for 

 some distance, giving off in their course short side branches 

 which terminate on the heart muscle cells. The terminal end- 

 ings of the side branches and the endings of the fibers differ in 

 complexity, as may be seen from Fig. 4. In (a) of this figure 

 is shown a very simple ending, the fine fiber terminating on the 

 muscle cell ending in two small end bulbs. In (^) and (c) of the 

 same figure are shown more complicated endings; the small 

 end-branch terminating in several secondary branches which end 

 in nodular end-swellings. 



That these endings are on the heart muscle cell may be 



