96 ANATOMY OF THE HEAD AND NECK. 



circumference is an orifice leading to the mastoid cells 

 below this aperture is a projection called the pyramid, froi 

 which a small spiculum of bone extends to the promontory 

 the apex of this pyramid is open, and from it emerges tl 

 stapedius muscle ; arching up from the pyramid, above t] 

 fenestra ovalis, is a ridge of bone marking the aqueduct 

 Fallopius. At the anterior part of -the circumference ai 

 the apertures of two canals, the upper one of which coi 

 tains the tensor tympani muscle, and the lower one tl 

 Eustachian tube. Between these two canals is a thii 

 osseous lamina, called the processus cockle ar if or mis. 



The Eustachian tube is the channel through which tl 

 tympanic cavity communicates with the fauces ; it is ai 

 inch and a half in length, and is partly osseous and parti; 

 cartilaginous in structure; its course in the temporal boi 

 is along the angle of union of the squamous and petrous 

 portions, external to the aperture which contains the cai 

 tid artery. Its cartilaginous portion has been alrea< 

 described (p. 62). 



The tympanum contains three small bones. They extern 

 in a line across the cavity, and are named malleus, incuf- 

 and stapes. 



The malleus, so called from its supposed resemblance 

 a hammer, is large at one end (head), and small and tape 

 ing at the other (handle) ; it has two processes, a long ai 

 a short; the short process springs from the root of tl 

 handle, and the long from a point just above it; the loi 

 process extends into the fissura Glaseri ; the handle is 

 tached to the membrana tympani ; upon the side of the he* 

 of the malleus is an articulating surface which unites it wil 

 the next bone, the incus. 



The incus, or anvil-shaped bone, consists of a body an< 

 two processes ; the body is concave, to receive the head of 

 the malleus ; the two processes, long and short, shoot 01 

 from the side of the body, opposite its articulating surfac 

 The long process terminates in a rounded extremity callc 

 the orbicular process, sometimes described as a sepan 

 bone, under the name of os orbiculare. The orbicular pi 

 cess unites the incus with the third bone, the stapes. 



The stapes, resembling in its shape a stirrup, has a base 

 and two sides which unite to form a head. The head is 

 marked by a superficial depression which articulates wi1 

 the orbicular process of the incus ; the base, which is a thii 

 osseous plate, is fixed over the fenestra ovalis. 



