VOL. XXX.] PHILOSOPHICAL TRANSACTIONS. 383 



The aqueduct is a flat tube, whose orifice is so situated between the two fore^ 

 mentioned cavities, that if there be any superfluous humidity contained in them, 

 it must needs be discharged, at least in this animal, into the mouth. This 

 situation of the aqueduct makes it plainly appear, that its use is to receive the 

 superfluous moisture from the cavitas tympani; for beside the glands fit for 

 separating such a quantity of humidity as may lubrify the muscles, and facilitate 

 both their motion and that of the ossicles, the very vapours that arise in such a 

 cavity as that of the tympanum in this animal, must at last be converted into a 

 liquor, and that must either again be received into the blood-vessels, or other- 

 wise discharged by such a receptacle as this. Some are of opinion that this aque- 

 duct is also assisting to the hearing, especially in men, because it is generally 

 obsei"ved that they who are deaf, open their mouths wide when they are desirous 

 to hear more distinctly; but I see not how that can be, for though the cavity 

 of the bony part of the aqueduct, in most of animals, is proportionally large 

 enough ; yet its carnous or fleshy part lies for the most part so flat, and its two 

 sides are so collapsed together, that scarcely any air can be admitted, at least so 

 far as to be subservient to the hearing. 



The ossicles in this, as in other animals, are 3, or rather 4 in number. The 

 malleolus is an irregular bone, and doubtless has been endowed with pretty large 

 .muscles, because of the rugosities, protuberances, and sinuses, observable in 

 it. It has a protuberant head, fig. 11, 4 lines broad, next to that a crena or 

 semicircular sinus (2), after which the bone is raised, affording a protuberant 

 margin to an oblong sinus (3), for receiving the head of the incus, 4 lines 

 broad. The opposite part of this sinus, or back part of the bone, is convex, 

 of an unequal rugous surface, with a great many protuberances and depressions, 

 for the origins and insertions of the muscles, for the space of 5 lines, where it 

 forms an angle, from whence it becomes flat and smooth, being 3 lines broad, 

 and reaching 4 lines to another angle (5), where the manubrium malleoli begins, 

 and where it becomes more round, from whence it gradually tapers to the point, 

 being 6 lines in length. 



The head of the incus is 4 lines broad, fig. 13, (l) below which is the neck 

 or an oblique sinus, (2) next to that are 2 apophyses, one on each side. These 

 descending obliquely outwards, and becoming flat, meet in a point, fig. 14, 

 (5), whence ascending obliquely inward, this production is joined to another 

 small round one, like the manubrium malleoli, 4-^ lines long (6). This has the 

 fore-mentioned small excavation or half round sinus (7), which with the extre- 

 mity of the stapes, I suppose to have contained the os quadrangulare, or rather 

 orbiculare, according to the figure of the sinus. 



The stapes differs much in figure from the human one. From its concave 



