texture, the muscular fibres appearing similar throughout the whole 

 surface ; without any central tendons as in the diaphragm, and chiefly 

 forming the internal layer, on which side they appeared most con- 

 spicuous. 



The blood-vessels of this membrane, the number of which is pro- 

 portionate to its action, resemble in a great measure those of the 

 iris, and are nearly as numerous. They anastomose with one another 

 in a similar manner, and their general dissection is from the circum- 

 ference of the membrane to the handle of the malleus. From near 

 this handle a small trunk sends off branches in a radiated manner, 

 which likewise anastomose with those that have an opposite course. 

 This correspondence in the number and distribution of blood-vessels, 

 between the membrana tympani and the iris, is given as a proof of 

 that membrane being endowed with muscular action ; and indeed the 

 author henceforth speaks without hesitation of a radiated muscle 

 distinct from the membrane. Having examined the structure of thia 

 muscle in various animals, Mr. Home found the application of a 

 principle laid down in a former lecture, namely, that while the orga- 

 nization necessary for muscular contraction may in some measure 

 exist in an apparent membrane, yet wherever muscular action is to 

 overcome a resistance, a fasciculated structure becomes absolutely 

 necessary. Thus in birds, where from the smallness of the organ 

 the resistance is very trifling, this membrane is of a simple structure, 

 like the coat of the hydatid; whereas in the elephant the fibres form- 

 ing fasciculi are very distinct and obvious. 



This muscular structure in the membrana tympani serves to ex- 

 plain various phenomena in hearing, which were not hitherto clearly 

 understood. It is observed that the sounds produced by percussion 

 on an extended membrane like the drum and tambourine, cannot but 

 be imperfect ; since, the tension being from side to side, the instru- 

 ment may be considered as consisting of a number of parallel strings 

 varying in their lengths like the parallel chords of a circle, and bear- 

 ing consequently no musical proportion to each other. Such also 

 must have been the imperfection of the membrana tympani, according 

 to the received opinion of its structure : but after the present disco- 

 very it will appear obvious that the radiated muscle proceeding from 

 the circumference of the circle to a common centre, produces a system 

 of strings all equal in length, and uniformly varying in musical effect, 

 according to their tension. 



In order to illustrate the manner in which this radiated muscle 

 adapts the membrana tympani to different sounds, the author finds 

 it necessary to enumerate the more important parts of the organ, 

 and to point out the use commonly assigned to each of them. 



Without entering into this detail, we can here only observe that, 

 availing himself of the present discovery, he compares the tensor and 

 radiated muscles of the membrana tympani to a monochord, of which 

 the membrane is the string, the tensor muscle the screw giving the 

 necessary tension to make the string perform its proper scale of vibra- 

 tions, and the radiated muscle acting upon the membrane like the 



