462 journal of Comparative Neurology and Psychology. 



Under the term membrana tympani I include the pars flaccida 

 (Shrapnell's membrane) and the pars tensa. The nerve sup- 

 ply to the membrana tympani is for convenience grouped as fol- 

 lows: 



I. Those entering at the region of the pars flaccida over the 

 plicae anterior and posterior. 



II. Those entering at the insertion of the membrane (Hmbus 

 membranae tympani) into the sulcus tympanicus. 



At both places the nerves, with a few exceptions to be noted 

 later, enter from the external auditory meatus under that part 

 of the cutis which is prolonged over the membrane. The rela- 

 tive number of fibers entering these parts appears to vary with 

 the species of animal examined. Thus, in the dog (Figs, i, 2 and 

 3) and the cat (Fig. 4), those entering at the periphery are very 

 abundant and exceed in number those entering at the pars 

 flaccida. In the monkey (Macacus rhesus, Figs. 5 and 6) there 

 are fewer and smaller peripheral bundles, influenced, I believe, 

 by the marked development externally of the tympanic bone 

 which is prolonged at an acute angle to a higher level than the 

 membrana tympani and forms a long osseous semicylindrical 

 external auditory meatus of relatively small diameter. In man 

 the distribution corresponds in many respects to that in the Maca- 

 cus though more fibers enter at the limbus. 



The bundles entering at the pars flaccida contain many medul- 

 lated fibers and have a general direction downward toward the 

 manubrium. Those entering at the limbus contain fewer medul- 

 lated nerves and radiate inward toward the manubrium, the larger 

 nerves following generally the direction of the radiating fibers of 

 the pars tensa. As the nerve distribution varies in the pars tensa 

 from the pars flaccida, it seems better to describe them separately. 



/. Pars flaccida. The nerves pass down under the cuticular 

 layer, not as one strand, but in detached bundles which freely 

 communicate with each other (Figs. 3 and 6). Their course is 

 directed toward the manubrium. The bundles pass over the 

 plicae anterior and posterior at varying points on to the upper part 

 of the membrana tensa. Numerous branches are given off from 

 these bundles which form a wide-meshed nonmedullated plexus 

 (ground, or fundamental plexus of the pars flaccida). From this 

 plexus numerous branches separate oflF which can be traced for a 

 varying length as follows: {a) To the membrana tensa, where 



