156 



Two months after conception, the oval hole, which forms the com- 

 mvmication between the vestibule or middle cavity of the labyrinth, 

 and the tympanmn, is, although very small, to be observed. About 

 the end of tlie third month, its circumference is ossified. In the sixth 

 month, it is as long and as perfect as at the ninth ; but not so broad. 

 I have not been able to remark any difference between the form and 

 size of the oval hole of the foetus at birth, and of the adult. But its 

 position varies ; for, in the foetus, it is comparatively nearer the poste- 

 rior side of the cavity of tlie tympanum than in the adult. 



The round hole, the medium of communication between the cochlea 

 or anterior portion of the labyrinth and the tympanum, is visible at the 

 same time as the oval hole. About the third month, its circumference 

 is ossified ; and, in the course of the sixth month, it is as large as in the 

 ninth, when it is equal in dimensions to what it will be in the adult, 

 but of a different fdrm ; for in the adult it is rounded, but in the 

 foetus it is triangular. 



We find, that the direction of the round hole is subject to great 

 variety ; and Scarpa,* who has paid very minute attention to its dis- 

 position in different subjects, is of opinion, that he has traced a con- 

 nexion between its direction and the age of ihe individual. He says 

 that, for some months after conception, this opening is directed rather 

 anteriorly ; that, at a more advanced period of uterogestation, it is 

 successively turned downwards and backwards ; that, at birth, its 

 aspect is nearly directly backwards ; and that it inclines itself more 

 and more in that direction till a certain period, when its aspect 

 changes, and is turned more outwards, so as to look towards the 

 membrane of the tympanum. These changes in direction are attri- 

 buted to the influence of the promontory and mastoid process. Before 



• Anatomicse Disquisitiones de Audito et Olfaclu. Auctore, A. Scarpa. 



