THE SKULL 275 



foramen, through which the internal carotid 

 artery enters the skull. 



iii. The auditory ossicles are most conveniently 

 examined with the bones of the auditory cap- 

 sules, on account of their close connection 

 with the organs of hearing ; though, morpho- 

 logically, they belong to the mandibular and 

 hyoidean arches. 



They form on each side a chain of small 

 bones, stretching across the tympanic cavity 

 from the tympanic membrane to the fenestra 

 ovalis. 



a. The malleus consists of a small body and two 

 processes. The larger process, or manu- 

 brium, is blade-like, and is attached along 

 the greater part of its length to the tym- 

 panic membrane, the tip being near the 

 centre of the membrane. The shorter pro- 

 cess articulates with a small fossa on the 

 inner surface of the tympanic bone. 



(3. The incus is a minute, somewhat pyriform 

 bone : its head bears in front a saddle- 

 shaped articular surface for the body of 

 the malleus, and is produced behind into 

 a short process, which articulates with a 

 fossa on the outer surface of the periotic 

 bone', just above the fenestra ovalis. 



The narrow end or stalk of the incus 

 projects downwards : its tip is bent in- 

 wards, and has attached to it a very small 

 bony disc, the os orbiculare. 



y. The stapes is a very small stirrup-shaped 

 bone, articulating by its arch with the os 

 orbiculare, and attached by its basal plate to 

 the membrane closing the fenestra ovalis. 



The morphological value of the auditory 

 ossicles has been much debated, and is not 



T 2 



