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the entire foetal life, but the nearer conception the more remarkable, 

 the petrous portion is marked by numerous eminences and exca- 

 vations ; owing to the labyrinth not being then so much covered by 

 bone as to hide its inequalities. The point of the petrous portion of 

 the bone, not prolonged beyond the cochlea, is, at this period, as 

 it were, tnincated and rounded. Of the excavations to be observed, 

 the most remarkable is one situated under the superior semicircu- 

 lar canal, and particularly noticed by Nesbit and Bichat. It is 

 also, in consequence of the small quantity of ossific matter covering 

 the labyrinth, that the internal auditory tube, although as wide at 

 birth as at any after period of life, is not as deep as it will be in 

 the adult. 



For a long time, there is a very striking difference between the 

 structure of the bone, which forms the parietes of the cavities of the 

 labyrinth, and that which covers them ; the former being, almost 

 from the moment of its first formation, extremely compact ; while 

 the latter, till nearly the ninth month, is very soft, spongy, and vas- 

 cular ; affording us an opportunity of examinnig with facility the 

 anatomy of the labyrinth, in consequence of tlie readiness with 

 which the spongy covering can be removed from the compact tissue 

 which forms its walls. 



In examining the development of the auditory cavities, our at- 

 tention is strongly roused by the want of connexion observed in the 

 growth of the different parts, which constitute them. The develop- 

 ment of many portions is so extremely rapid, that, at the ninth month 

 after conception, they have those dimensions which they are to enjoy 



