THE SYMPATHETIC SYSTEM. 589 



or close the posterior nares, and accomplish a similar office with the 

 muscles already named in front. The levator palati and uvular muscles 

 are supplied by filaments from the spheno-palatine ganglion, and are 

 involuntary in character. 



The ear has two sets of muscles, similarly supplied. The superficial 

 set are those attached to the external ear. They are comparatively 

 inactive in man, but in many of the lower animals are well developed 

 and important. In the horse, the deer, the sheep, and various other 

 species, they turn the ear in different directions to catch more distinctly 

 feeble sounds, or to exclude those which are disagreeable. These mus- 

 cles are supplied by filaments of the facial nerve, and are voluntary in 

 their action. 



The deep-seated set are the muscles of the middle ear. Sounds are 

 transmitted to the middle ear through the membrane of the tympanum, 

 which may be made more or less sensitive to sonorous impressions by 

 varying its condition of tension or relaxation. This condition is regu- 

 lated by the two muscles of the middle ear, namely, the tensor tympani 

 and the stapedius. The first named muscle is supplied with nervous 

 filaments from the otic ganglion of the sympathetic. By its contraction, 

 the handle of the malleus is drawn inward, bringing the membrana tym- 

 pani with it, and thus increasing its tension. On the relaxation of the 

 muscle, the chain of bones returns to its ordinary position, and the pre- 

 vious condition of the tympanic membrane is restored. This action, so 

 far as we can judge, is purely involuntary. The stapedius muscle, on 

 the other hand, is supplied by a branch of the facial nerve (p. 549). It 

 is probable that its contraction serves to relax the membrana tympani, 

 and enables us to make a certain degree of voluntary exertion in listen- 

 ing for faint or distant sounds. 



Connection with the Circulation. Perhaps the most important fact 

 concerning the sympathetic S3 r stem is that of its influence over the 

 vascularity of the parts supplied by it. In the first place, division of 

 the sympathetic trunk produces a vascular congestion in the corre- 

 sponding parts. If this nerve be divided, in any of the warm-blooded 

 quadrupeds, in the middle of the neck, a vascular congestion of all parts 

 of the head, on the corresponding side, immediately follows. This con- 

 gestion-is most distinctly evident in the rabbit, in the thin and trans- 

 parent ears; and within a few minutes after the operation, the difference 

 in their appearance on the two sides is strongly pronounced. All the 

 vessels of the ear on the affected side become turgid with blood ; and 

 many which were before imperceptible, are distinctly apparent. This 

 effect, which was first pointed out by Bernard, and has been observed by 

 many other experimenters, we have often verified. It lasts for a con- 

 siderable time, and may even be very distinct at the end of three weeks. 

 It remains longer when a portion of the nerve has been cut out, or the 

 cervical ganglion extirpated, than when its filaments have been simply 

 divided by a transverse section. It finally disappears when the separated 

 filaments have reunited and regained their functional activity. 



