382 



SCIENCE. 



[Vol. I., No. 14. 



iioid fissure. It is produced below into a sharp, 

 irregular ci'est, the vaginal process, variablj- 

 extended into several uneven points. 



Tiie outer portion of the tj'mpanic plate is 

 produced into a cylindrical scroll, which forms 

 the floor and sides of the external auditory 

 meatus. The rough, crescentic border at the 

 entrance of the latter is the auditory process, 

 and gives attachment to the auricle. The 

 scroll terminates at the inner extremity of the 

 meatus witii an abrupt tymjMnic margin (fig. 

 1, a), which is grooved along its course within 

 for the insertion of the tympnnic membrane. 



The inner extremity of tlie tympanic plate 

 closes the lower part of the eustachian tube. ' 



Back of the vaginal process, and partially 

 sheathed by a downward extension of the 

 same, is the usually conspicuous styloid pro- 

 cess. This is a narrow, tapering spine, of 

 variable length, from half an inch to an inch 

 or more, directed from the petrosa downward, 

 forward, and inward. Before maturity it is 

 commonly a distinct bone, ^joined by cartilage 

 to a short cylindrical base,- which occupies a 

 pit or groove embraced by the vaginal process. 

 Prior to pubertj' it is, for the most part, car- 

 tilaginous, and is usuall3r lost in prepared spe- 

 cimens of the temporal bone. 



. Between the stj'loid and mastoid processes 

 is the stylo-mastoid foramieyi, which is the exit 

 of the facial canal. Behind it is a broad, 

 mostly quadrate, ai-ticular facet, which joins the 

 jugular process of the occipital bone. Adja- 

 cent, inwardly, is the jugular fossa , a concave 

 recess of variable capacitj^, and commonly dif- 

 fering proportionately from that of the oppo- 

 site bone of the same skull. It accommodates 

 the commencement of the jugular vein, nnd 

 forms the fore-part of the outer division of the 

 jugular foramen. To its inner side is a pyram- 

 idal pit, which communicates at bottom with 

 a fine canal," extending to the cochlea, for the 

 passage of a vein. The mouth of the pit ex- 

 tends downwai-d in a groove, which forms the 

 fore-part of the inner division of the jugular 

 foramen. 



Inwardlj' from the lower extremitj^ of the 

 jugular fossa, and behind the inner extremity 

 of the vaginal process, is the entrance of the 

 carotid canal. This ascends verticallj-, and 

 then curves abruptly inward, and proceeds to 

 the apex of the petrosa. It is sometimes in- 

 complete at its inner fore-part, when, in the 

 recent state, it is closed b3' fibrous membrane. 

 It gives passage to the internal carotid artery 

 and sympathetic nerve. 



Stylo-hyal. 



Tympano-hyul. 



The uneven surface beneath the apex of 

 the petrosa, at the fore-part, gives origin to the 

 elevator of the palate, and, just behind, gives 

 attachment to the pharynx. Back of this, the 

 irregularly grooved part joins the occipital 

 bone, having the interval occupied by flbro- 

 cartilage. 



The external auditory meatus, or outer pas- 

 sage of the ear, in the prepared bone, communi- 

 cates at bottom with the tympanic cavit}-. It 

 is a curved canal, with the convexity- upward, 

 and is about two-thirds of an inch in length. 

 It is directed from without inward, and a little 

 forward and downward. Its cross-section is 

 oval, with the longer diameter inclined forward. 

 The roof, formed by the auditory plate, is ex- 

 tended to the greatest degree outwardly ; while 

 the floor and sides, formed hj the tympanic 

 plate, are extended most inwardly. The en- 

 trance is formed above bj- the narrowing of the 

 liroad arch of the auditor^- plate, and below bj- 

 the auditor}- process curving up at the sides to 

 the roof of the meatus. The tympanic orifice ' 

 (fig. 1, a), or communication with the tym- 

 panic cavit}', is oval, or nearl}' circular, and 

 A'ery oblique, with its plane inclined outward 

 and downward to an angle of about 50°. It is 

 formed above hy the sharp, curved tympanic 

 margin of the anditorj' plate, and below by the 

 horseshoe-like tympanic margin of the tym- 

 panic plate, grooved within for tlie insertion 

 of the tympanic membrane. 



The glenoid fissure - defines the tj-mpanic 

 plate from the fore-part of the squamosa, behind 

 the glenoid fossa, and remains as a portion 

 of the petro-squamosal suture. Its outer part 

 is closed by anclij-losis of the tymi)anic plate 

 with the post-glenoid process. Its inner part 

 receives a bar, dipping into it from the tegmen 

 of the petrosa, and separating the t3'mpanic 

 plate from the squamosa. At its middle is a 

 foramen, — the exit of a short, oblique eanaP 

 from the tympanum, for the accommodation 

 of the long process of the mallet and the 

 tympanic cord. 



The eustachian tube is a shoi't, oblique canal, 

 communicating outwardly with the tympanum, 

 and opening inwardly in front of the apex of 

 the petrosa, at the notch between this and 

 the squamosa. It is formed in front and be- 

 neath bj' the inner extremit}' of the tymijanic 

 plate, above by the tegmen, and behind by the 

 anterior wall of the carotid canal. Its inner 

 extremitj' is roughened for the attachment of 

 the cartilaginous portion of the tube. 



Auertura tyrapanica. 

 i Fissure of Glaser; Glaeorian fissii 

 ' Canal of Hiiguier. 



