464 'Journal of Comparative Neurology and Psychology. 



the monkey (Fig. 5) and man, over the posterior plica. The 

 main trunks when they reach the manubrium may continue down 

 one side or may divide and send a branch down each side, con- 

 nected by a plexus of fibers across the external surface of the man- 

 ubrium. From the large nerve bundles, branches pass off as 

 follows: {a) Over the external and internal surface of the manu- 

 brium forming an external and internal manubrium plexus (Figs, i, 

 5 and 4). (b) At intervals branches pass off which radiate toward 

 the periphery (limbus tympanicus). Each of these with little or 

 no medullary sheath, is of considerable size near the manubrium, 

 but as at repeated intervals along its course it gives off branches, 

 it finally arrives at the limbus as a very fine fiber. The branches 

 which these radiating nerves give off are mostly nonmedullated; 

 they frequently divide and interlace with each other to form in the 

 membrana propria wide-meshed plexuses, the ground or funda- 

 mental plexus. This plexus lies among the circular and radiating 

 connective tissue bundles and connects with the subepithelial and 

 submucous plexuses. 



(2) The nerves from the external auditory meatus at the limbus 

 enter all around the periphery (Figs. 4 and 5). As they approach 

 the limbus they divide and form a dense plexus with branches 

 from the corresponding adjacent nerves. This annular or zonu- 

 lar plexus lies both external and internal to the limbus (Fig. 2). 

 From this plexus or from the main trunks fibers pass (a) chiefly 

 into the membrana tensa and {b) a few into the tympanic cavity 



(Fig. 4)- 



(a) Those passing to the membrana tensa are directed toward 

 the manubrium lying among the radiating connective tissue bun- 

 dles. At the periphery the nerves are of considerable size, but as 

 they pass forward branches are given off which enter into the 

 adjoining ground plexus so that when ultimately they reach the 

 manubrium they appear as very fine fibers which pass into the 

 plexuses on or around the manubrium (Fig. i). 



(b) Those passing into the tympanic cavity can be traced into 

 the plexus in its mucous membrane. 



The ground plexus is a wide-meshed interlacing of nerves lying 

 in the fibrous tissue and corresponds to the ground plexus of the 

 pars flaccida. The nerves which compose it come almost entirely 

 from the external auditory meatus, those coming from the middle 

 ear being few in number. It ought to be regarded as the chief 



