ORGAN OF HEARING IN MAMMALIA. 



243 



188 



long cms of the incus, and descending to the c fissura Glasseri,' 

 makes its exit by the contiguous canal and foramen, descending 

 mesiad of the ascending mandibular ramus to join the lingual nerve. 

 Within the tympanum it receives filaments from the tympanic 

 branch of the trigeminal. The facial nerve gives a branch to the 

 stapideus muscle. From a ganglion of the pneumogastric is sent 

 off the ( ramus auricularis,' which is joined by a filament from the 

 glosso-pharyngeal, and is conducted by a groove in the jugular 

 fossa to the f aqueduct of Fallopius : ' here filaments are sent to 

 join the facial, and one to the nerves of the meatus and ear-conch. 

 The tympanic nerve derived from the ( petrous ' and ( otic ' 

 ganglia, enters the tympanum near the anterior margin of the 

 ' fenestra rotunda,' traverses the groove on the promontory, and, 

 near the ' fenestra vestibuli,' enters the osseous canal which leads 

 to the surface of the petrosal in front of the ( hiatus Fallopii,' and 

 passes to the otic ganglion. From this gan- 

 glion a nerve is sent to the tensor tympani. 

 The ( meatus auditorius externus,' fio\ 



* 



188, is formed by bone, g, for a short 



extent from the drum-membrane, />', is 



chiefly cartilaginous in the rest of its extent, 



but is membranous above and behind, and 



there perforated by the orifices of the ceru- 



minous follicles, o, p. The canal has an 



oval area, is about an inch and a quarter in 



length, and is lined by a continuation of the 



skin of the auricle. This skin becomes more 



delicate as it approaches the osseous part 



of the passage extremely so where it is continued 011 the 



outer surface of the membrana tympani. The skin of the 



auditory passage is covered with fine hairs, and these become 



developed at the outlet into long defensive cilia or ear-lashes. 



The ' fflandulae ceruminosae ' are small round or oval bodies of 



o 



a brownish-yellow colour, and very vascular. They are im- 

 bedded in the areola3 presented by the dense cellular tissue 

 which connects the skin of the auditory passage to the subjacent 

 cartilage or bone. The ear-wax, cerumen, is, as is known, a 

 thick orano-e-coloured or yellowish-brown viscid substance, of an 



o +> 



extremely bitter taste, and somewhat aromatic odour. \Vhen 

 first secreted, it is a thin, yellowish, milky fluid. It is an accessory 

 defence against the entry of insects into the meatus. The ear- 



O / 



drum closes the meatus obliquely from above downward and 

 inward ; the bony part, </, of the meatus forms a gentle curve, 



Horizontal section of the audi- 

 tory passage (meatus auditorius 

 externus). xcvin". 



K 2 



