416 ORGANS OF THE SENSES. 



a little below them, strange and unexpected reflex phenomena 

 will follow, such as a feeling of nausea, or of uneasiness and 

 general discomfort, which warns us of the danger to which 

 the organ of hearing is exposed ; these are, in short, phe- 

 nomena of general sensibility, and have no connection with 

 the sense of touch. In this canal (in its cartilaginous and 

 fibrous portion) are found the ceruminous glands ; we ex- 

 amined the secretion of these glands, when studying the 

 functions of the skin, and found it the thickest and most 

 sticky of the secretions of perspiration: this cerumen serves 

 to prevent any substance from reaching the bottom of the 

 external auditory canal, where its presence would be injuri- 

 ous to the membrana tympani. 



B. Middle chamber of the ear. 



The membrana tympani is formed of connective and elastic 

 fibres, and contains a large number of vessels ; here, as in the 

 case of the pinna of the ear, the abundance of the vessels 

 appears to be intended for the purpose of keeping up the 

 temperature of these parts which are always uncovered and 

 exposed to that air from which they receive vibrations. The 

 membrana tympani is essentially a collecting organ ; it is 

 situated at the bottom of the external auditory canal, but 

 does not share in the peculiar sensibility of the latter : if an 

 insect penetrates so far as to touch it, no reflex phenomenon is 

 produced, but only a sensation resembling that accompanying 

 a sound, and which is caused by the vibrations communicated 

 to it. It is, therefore, simply a physical organ, for the recep- 

 tion of air, or of the sonorous vibrations from the walls of the 

 canal. 



This membrane is not normally so situated as to collect 

 the waves of sound, but appears, on the contrary, to avoid 

 them up to a certain point, being oblique from top to bottom 

 and from back to front ; it seems, in short, to continue the 

 supero-posterior wall of the canal; the younger the subject 

 the more decided the obliquity, while in the fcetas this mem- 

 brane is nearly horizontal. It is not a plane, but consists of 

 a very low cone, having its internal summit slightly flattened, 

 and its edges attached to the deep opening of the external 

 auditory canal ; it is enclosed in a sort of frame which appears 

 distinctly in the form of an imperfect ring in young subjects. 

 This me'mbrane is, therefore, convex on the interior, its con- 

 vexity being preserved by a chain of small bones, a portion 

 of which (the handle of the malleus) is contained in the thick 



