378 DEVELOPMENT OP THE EAR. 



though, from our ignorance of what it is in which quality consists, we are 

 wholly unable to offer an explanation of the precise mode of action of 

 that part of the auditory mechanism. 



We are so prone to extend our ideas of our own perceptions to the 

 Partial deaf case ^ otner animals that it may not here be unprofitable to 

 ness of inferior offer a remark which may serve to correct such views. To 

 many of the sounds with which we are familiar, birds and oth- 

 er lower tribes are totally deaf; they can not appreciate, except within a 

 narrow range, the notes of music, and, indeed, to all those in which there 

 is no cochlea such notes are inaudible. - In the lower grades nothing more 

 than a noise can be detected, and that doubtless in a very indefinite way. 

 We can therefore understand how, through imperfection of construction, 

 they are cut off from the perception of an infinite number of occurrences 

 which are obvious enough to us. Even among our domestic animals, to 

 which we so often speak or sing in the way we do to one another, the in- 

 tellectual obtuseness which we think we recognize doubtless originates 

 in an incapacity to receive those expressions, because of faulty structural 

 condition. 



In closing these remarks on the sense of hearing, it is necessary to 

 , direct attention to the order of development of the organ in 



Order of devel- ,.,,,,,,, . r & 



opment of the the individual of the human species, as we have done in the 

 case of the successive tribes of animals ; and here it may be 

 affirmed that the ear of man passes in a transient succession through all 

 these permanent animal forms. It originates at first from a budding 

 forth of the vesicle of the medulla oblongata, the issuing cell becoming 

 by degrees pear-shaped, and connected with the parent cavity by a thread 

 or stalk. The pear-shaped cavity is the rudiment of what is eventually 

 to be the vestibule ; the pedicle will become the auditory nerve. Even 

 at this early period the cavity contains an otolith. By degrees there 

 arises from the folding in of the walls of the vestibule the curved forms 

 that are to become the semicircular canals, and, at a period a little later, 

 in an analogous way, the cochlea. At one stage of this development the 

 membranous labyrinth presents an almost identical aspect with that of 

 the retina at the time, both being composed of a fibrous network inter- 

 spersed with granules and nucleated cells, the shadowing forth of the 

 parallelism of construction which may be traced in the two organs when 

 they have reached their utmost development, the one for the cognizance 

 of normal and the other for transverse vibrations. 



And so it appears that, as respects the organ of hearing, its order of 

 illustration of development in the individual is identically the same as its 

 the imperfec- order of development in successive tribes taken in the ag- 



tionofthedoc- _ r _ _ . 



trine of means gregate. In the latter case, we constantly regard its con- 

 and ends. dition of construction as arising from a purposed adaptation 



