528 AXATOJUIC^lL TECHNOLOGY. 



§ 1434. Tympanum s. Auris media. — With nippers remove the 

 wall of the mesal chamber of the tympanic bulla (Fig. 58), and 

 note the delicate membrane lining it, also the bony septum (Fig. 58, 

 Spt. tym.) separating this chamber from the tympanum proper 

 except at a point directly ventrad of the fenestra rotunda, where it 

 is notched, thus forming a free communication between the two 

 chambers of the bulla (Fig. 58). CarefuUy remove the septum with 

 nippers and use the scissors for cutting its lining membrane, so that 

 nothing may be removed by inadvertence. Holding the head in 

 the hand, allow the light to fall upon the tympanum from various 

 directions. Note the attachment of the membrana tympani to a 

 ring of bone terminating the ectal bony meatus, and that the mem- 

 brane is conical in form, the apex projecting into the tympanum. 



§ 1435. Canalis Eustachiana (Fig. 58, 88). — This, as stated 

 above (Fig. 88), is the canal connecting the pharynx and tympa- 

 num. Insert a beaded bristle into the pharyngeal opening (Fig. 88) 

 and it will appear at the tympanic opening in the cephalic part of 

 the tympanum, just dorsad of a projecting shelf of bone. 



Ossicula auditus, Bones of the Ear (Fig. 127). — There are three 

 of these, malleus, incus and stapes, extending in a chain from the 

 membrana tympani to the fenestra ovalis. 



§ 1436. Malleus, hammer (Fig. 127).— The malleus is the first 

 of the chain of ear bones. Its handle stretches partly across the 

 membrana tympani. With the tracer move the handle ; it will 

 sway but little. Note that the neck and head of the malleus form 

 an angle with the handle, and that attached to a small cylindrical 

 process of bone arising from the mesal aspect of the neck, is the 

 short tendon of the tensor tympani muscle (the M. EustacManus 

 of Straus-Durckheim, A, II, 200). This muscle is nearly spherical 

 and occupies a concavity slightly cephalad of the fenestra ovalis. 

 The fossa may be seen on a prepared skull. With scissors cut the 

 tendon of the muscle and then the dorsal part of the bony ring sup- 

 porting the membrana tympani, and carefully remove the malleus 

 adhering to the membrana. Note the rounded head of the malleus 

 and also the long flat process (processus gracilis) arising from the 

 lateral aspect of the neck. 



§ 1437. Incus, anvil (Fig. 127). — This, the second of the chain 

 of bones, resembles a molar tooth with two divergent fangs rather 

 than an anvil (Quain, A, II, 631). To expose it, remove the cephalic 

 part of the tympanum and the tensor tympani muscle. Examine 



