384 LABORATORY MANUAL OF HUMAN ANATOMY 



note that the cortical substance (substantial corticalis) is soft 

 while the central part or nucleus of the lens (nucleus lentis) is 

 firmer. Place a bit of the lens in thirty-three and one-third 

 per cent, alcohol for twenty-four hours, then tease it apart and 

 under the microscope examine 



(a) Epithelium of lens (epithelium lentis). 



(b) Fibres of lens (fibrae lentis). 



Chambers of Eyeball (Camerae oculi). 

 These are two in number : 



(a) Anterior chamber of eyeball (camera oculi anterior). 



(aa) Angle of iris (angulus iridis) (0. T. iridocorneal angle). 



Why is this of great importance ? 

 (6) Posterior chamber of eyeball (camera oculi posterior). 



Study the form, position, and boundaries of each. Both con- 

 tain the so-called aqueous humor. 



ORGAN OF HEARING (ORGAN ON AUDITUS). 

 This consists of several parts, viz. : 



(a) Internal ear (awn's interna). 



(aa) Membranous labyrinth (labyrinthus membranaceus) . 



(ab) Osseous labyrinth (labyrinthus osseus). 



(b) Middle ear. 



(ba) Cavity of tympanum (cavum tympani). 



(bb) Eustachian tube (tuba auditiva [Eustachii]). 

 (be) Mastoid cells (cellulae mastoideae). 



(c) External ear (auricula) (0. T. pinna). 



The dry temporal bone should be thoroughly reviewed in con- 

 nection with the study of the organ of hearing. The external ear 

 has been studied already. (Cf. p. 258.) 



Take a temporal bone, preferably one with the auricula still 

 attached. to it; saw off the squama temporalis by making a 

 horizontal cut at the level of the root of the zygomatic process ; 

 remove roof and anterior wall of the external acoustic meatus 

 piecemeal, with the aid of bone-forceps and chisel, until the mem- 

 brane of the tympanum is exposed. 



