332 ZOOTOMY. 



internally by the periotic, externally by the tympanic 

 membrane, below and at the sides by the tympanic bone. 



349. The auditory ossicles (see 73 76) : after 

 observing them and their muscles ( 352, 353) in situ, they 

 should be removed, and examined under a low power of the 

 microscope. 



350. The fenestra ovalis and fenestra rotunda 



( 56). 



351. Tne aperture of the Eustachian tube on the 

 inner wall of the tympanum, below and anterior to the 

 fenestra ovalis (see 55, p. 272, and 370, p. 336). 



352. The tensor tympani, a small muscle inserted by a fine tendon 

 into the malleus : it arises from the alisphenoid. 



353. The stapedius, a still smaller muscle, arising from the surface 

 of the periotic, just above the fenestra rotunda, and passing forwards to 

 be inserted into the neck of the stapes. 



354. By the removal of the bulla tympani the proximal portions of 

 the vagus and hypoglossal nerves ( 244, 246) are exposed and may be 

 traced to their foramina of exit from the skull ( 43, 58). 



355- Lying immediately in front of and parallel to the hypoglossal is 

 a much slenderer nerve, the glossopharyngeal : it makes its exit from 

 the skull with the vagu?. 



356. The spinal accessory or eleventh nerve leaves the skull along 

 with the glossopharyngeal and vagus, and passes backwards to its 

 distribution to some of the muscles of the neck. 



XLIV. Dissect off the masseter : carefully detach the 

 ascending portion of the mandible from the 

 pterygoid muscles which are inserted into its 

 inner surface: with bone-forceps cut away the 

 portion of the mandibular ramus lying posterior to 

 the inferior dental foramen ( 71) : make out : 



357. The third division of the fifth or mandibular nerve, supply- 

 ing the muscles of the lower jaw and sending a branch the gustatory 

 nerve to the tongue : the main trunk is continued through the 

 inferior dental foramen to the interior of the ramus and so to the 

 teeth. 



