STAPES. 529 



under a strong light with a magnifier. Note the larger part with its 

 concavity for articulation with the malleus and, extending ventro- 

 mesad, a slender process which articulates with the stapes. Con- 

 tinue to use the magnifier, and with a tracer sever the connection 

 with the stapes ; then, by moving the incus slightly, it will be seen 

 to occupy the caudal part of an elongated fossa caudo-laterad of the 

 one occupied by the tensor tympani muscle. The shorter process 

 (fang) is held in position by a ligament. The cephalic part of the 

 fossa is occupied by the head of the malleus. Carefully nip away 

 the lateral wall of the tympanum and fully expose the longer pro- 

 cess of the incus and its ligament. 



§ 1438. Stapes, stirrup (Fig. 127).— This is the third and last of 

 the chain of bones. (The so called Os lenticulare between the 

 stapes and incus belongs properly to the incus.) The narrow part 

 of the stapes, termed the head, articulates with the longer process 

 of the incus, and its broader part or base is inserted into the foramen 

 ovale. With the tracer or forceps move the bone slightly from side 

 to side, and there will be seen passing caudo-laterad the tendon of 

 the M, stapedius. Remove the lateral wall of the tympanum, the 

 mastoid process, etc., around the Fm. stm. (Fig. 57), and the muscle 

 will be seen to originate near the aquseductus Fallopii (§ 506) entad 

 of the 7th nerve. On the prepared skull the space occupied by the 

 stapedius may be seen to be separated from the fossa occupied by 

 the incus by a septum of bone. After the muscle is well made out, 

 grasp its tendon and pull gently. The stapes will be drawn out of 

 the fenestra ovalis. Note the small bony process on the caudal side 

 to which is attached the stapedius muscle. 



LABYRINTHUS s. AURIS ENTALIS (INTERNA). (Fig. 127.) 



§ 1439. Fenestra rotunda s. Fenestra cocMece ; Fenestra ova- 

 lis s. Fenestra mstihuU. — These two gateways to the labyrinth have 

 already been exposed. Note the membrane covering the fenestra 

 cochleae. The fenestra vestibuli was closed by the base of the 

 stapes and its connecting soft parts. These foramina open respect- 

 ively on the summit and side of the cylindrical cochlear eminence. 



§ 1440. Cochlea. — The cochlea is situated mainly in the cylin- 

 drical elevation at the caudo-lateral aspect of w^hich is found the 

 Fenestra rotunda s. cochleae. It consists obviously of the tapering 

 canals (scalae) separated by a lamina of bone (lamina spiralis, Fig. 

 128). These scalse are coiled about a central piece (modiolus), some- 

 34 



