NERVES AND VESSELS OF THE EUSTACHIAN TUBE. 83 



size and number in the different classes of animals. Whilst in 

 the Quadrumana, in Bats and Marmots, and in the Sheep and 

 Goat, they form a thick layer either limited to certain spots or 

 completely invest the tuba on its central and median side, they 

 appear to be reduced in all the other animals I .have examined 

 to a thin layer in the submucous layer. The only histoiogical 

 difference I have been able to distinguish between them is in 

 regard to their size. 



4. NERVES. 



I have already described ganglion cells as occurring in the 

 nerves of the mucous glands of the Eustachian tube of Man. 

 The nerve fasciculi consist of double-contoured fibres, and ori- 

 ginate in the plexus tympanicus and the plexus pharyngeus, 

 forming a coarse network which contains a variable number of 

 ganglion cells at those points where the fasciculi meet. The 

 cells vary in size, and their processes are continuous with 

 primitive fibres. The ganglia agree with those that occur 

 in the branches of the plexus promontorii (E. Bischoff) ; and 

 since the nerves of the Eustachian tube essentially originate in 

 this plexus, while they also contain sympathetic nerves, we 

 cannot well deny their morphological relation to the tympanic 

 plexus, although their possible functional importance in re- 

 gard to the mucous glands is on this account by no means 

 excluded. 



5. VESSELS. 



The vessels of the Eustachian tube arise from two different 

 sources; namely, from the vessels of the tympanic cavity, and 

 from those supplying the wall of the pharynx : the latter pre- 

 sent no peculiar features in their arrangement, but agree in 

 their characters with the pharyngeal vessels. 



The former, on the other hand, run in the first place as large 

 arterial trunks in the direction of the long axis of the tube, 

 both upon its lower part and upon the safety tube, and in 

 transverse sections constantly appear at certain definite points. 

 Thus, in the processes of the mucous membrane situated be- 

 tween the safety tube and the accessory fissure, two vessels of 

 different size become apparent, of which one arises upon 



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