ORGAN OF HEARING IN MAMMALIA. 24i 



long crufi of fehe incus, and descending to the ' fissura Glasseri,' 

 makes its exit by the contiguous canal and foramen, descending 

 meaiad 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 ( 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 

 4 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 Faliopii,' and 

 passes to the otic ganglion. From this gan- 

 glion a nerve is sent to the tensor tympani. 

 The * meatus auditorius externus,' fig. 

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

 extent from the drum-membrane, h, 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 



i . r .1 • l mi • 1*1 Horizontal section of the audi- 



skin oi the auricle. Inis skm becomes more t ory passage (meatus auditorius 

 delicate as it approaches the osseous part externus). tarmr. 



of the passage — extremely so where it is continued on 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 ' glandula? ceruminosa? ' are small round or oval bodies of 

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

 bedded in the areola) 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 orange-coloured or yellowish-brown viscid substance, of an 

 extremely bitter taste, and somewhat aromatic odour. When 

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

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

 drum closes the meatus obliquely from above downward and 

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



