384 PHILOSOPHICAL TRANSACTIONS. [aNNO]718. 



extremity it is enlarged on each side by two small slender productions, not unlike 

 the processes of the vertebrae of some fishes, fig. 13, (22) to which is joined 

 the basis (3), as thin almost as the scale of a fish. This was accidentally sepa- 

 rated from its two sides, and remained in the foramen ovale, from whence I 

 pulled it with a pin, it is concave towards the stapes, and convex toward the 

 vestibulum. 



The foramen ovale lies so hid and obliquely in the side of the cavitas tympani, 

 that it could not be delineated in its true dimensions. Near it is another hole, 

 oblong and sharp at both ends, both which give an entry into the vestibulum. 



The vestibulum is of an irregular figure, fig. 17, (a); it is for the most part 

 3 lines from the one side to the other, and perforated by 8 orifices, viz. 5 for 

 the canals of the labyrinth, fig. l6, 17, (a) 1 for the cochlea, fig. 17, (h), and 

 2 for the fenestras (b,c). 



The cochlea is a long cavity consisting of 3 gyres or meanders, fig. 18, (def). 

 Its orifice, where it proceeds from the vestibulum, is but small; but it after- 

 wards widens, so that the first course of this cavity is a third part larger than 

 the second (e), and proportionally the third is less than the other two (f), till 

 it terminates in an orifice (g) situated in the top, for receiving a branch of the 

 soft portion of the nervus auditorius, which accompanies and passes along all 

 its gyres. ^ 



The hardness and solidity of the bone, from which it may be justly called 

 OS petrosum in this subject, was such that I could not exactly trace the three 

 canals or ducts of the labyrinth, so as to give a true idea of the manner of their 

 several turnings. But Valsalva's figures of the human ear directed me so ex- 

 actly, that I easily found out the several orifices, and opened them so far as to 

 find out their situation and true dimensions, by introducing a hog's bristle, then 

 cutting it off and stretching it out to the scale. Thus after laying open the 

 two foramina which gave an inlet to the vestibulum, I soon perceived the several 

 orifices, which in so large a subject were pretty conspicuous. I first turned to 

 the one hand and discovered the duct of the cochlea; this I pursued all along 

 the protuberance, fig. 10, (d); in doing of which I laid wholly open the lesser 

 duct of the labyrinth, fig. l6, 17, (d). Then turning up the other side of the 

 bone, I traced the soft portion of the nervus auditorius, divided into two 

 branches, one distributed into the cochlea, and the other to the labyrinth. In 

 filing the bone a little further, I opened a small part of the middle duct, and 

 soon discovered the ductus major ; after which I measured their several lengths 

 as is said. 



The labyrinth then consists of three lineae semilunares or incurvated ducts, 

 whereof the major lies in that part of the processus petrosus, which regards the 



