THE EAR. 



395 



Part (if the outer wall of the perilymphatic space 

 after Retzius. Vériok's Syst., Obj. Ill, Oc. 3. 

 per. Periosteum. 

 pg. Perilymphatic network. 

 zi'i. Leucocytes. 



and rapidly wideu.s to form a short, flattened, blind sac (saccN-^ 

 fenestrae ovalis), which is lodg-ed in the fossa {sfo). Its walls are 

 thin and pig-mented. 



(2) The ductus perilym- 

 phaticus (Hasse), (Fig-. 245 

 tl]}) passes above and behind 

 the ductus fenestrae oval'is, be- 

 hind the auditory nerve, and 

 near the cochlea, then behind 

 and above the lagena to the 

 aqnaeductiis cochleae (Fig. 244 

 ac'), where it forms a short, 

 wide tube, which passes back- 

 wards and inwards through 

 this canal to the canalis jiigu- 

 laris ; here it lies close to the 

 nerves and forms a short oval 

 sac {saccus per'ilymjjhatlcns) {dp), which communicates with the sub- 

 arachnoid space of the cranial cavity by means of a tube from the 

 neck of the sac. The walls of this structure are thin and formed of 

 connective-tissue with very few pigment-cells. The other extremity 

 of the tube passes to \\\q parshasïlans2ivA under the shins post, utri., 

 between it and the pars neglecta ; it then courses to the outer side 

 of the hinder end of the external semicircular canal : the tube 

 then bends downwards to the outer side of the utricle and saccule to 

 open into the general perilymphatic space. 



d. The membranous labyrinth (Figs. 247, 248) has the fol- 

 lowing* parts : the utricle and sinus Siiperior, the recessus utrlculi, 

 the anterior semicircular canal and anterior ampulla, the external 

 semicircular canal and external ampulla, the posterior semicircnlar 

 canal and the posterior ampulla, the saccule, ductus endolympiliaticus, 

 and saccus endolymphaticiis, the pars neglecta, the lagena cocJdeae, the 

 p)ars hasilaris cochleae, and the so-called tegmentnm vasculosum. 



In addition the following nerve-terminations can be distinguished : 

 (i) The macula ac. recessus utrieuli, (3) the three cristae acusticae am- 

 jnilloriim, (3) the macula ac. sacculi, (4) the macula ac. neglecta, (5) the 

 pjapUla ac. lagenae cochleae, and (6) the papilla ac. basilaris cochleae. 



The auditory nerve divides immediately beyond its origin from 

 the medulla ohlongata to form a ramvs anterior m\d a ramus posterior, 

 which course alongside each other for a short distance, the latter 

 lying behind and above the former. The R. anterior runs forwards 



