194 



THE «KIN AND THE SENSE-ORGANS. 



periclioudrium lining this cavity form a very delicate, pigmented 

 membrane, formed of nmnerous fine elastic fibres which cross each 

 other irregularly; its inner surface is lined with an incomplete 

 layer of branched protoplasmic cells with large oval nuclei. From 



Fig. 245. 



j^er s. 



The membranous labyrintli of Rana csculenta, \\dthin its natural covering of periosteum ; 



after Retzius. 



I. Seen from the side ; magnified tea times. 



II. Tlie hinder haJf ; magnified ten times. Seen obliquely from above, and in front, and from 



the side. 



ndf 

 al. 

 tip. 

 apb. 



cp 



ctfo 



dp 



dp' 



I. 



ms. 



Anterior ampulla. 

 Apertura fenestrae ovalis. 

 Apertura lagenae. 

 Posterior ampulla. 

 Opening into the pars basilaris. 

 Anterior semicircular canal. 

 External semicircular canal. 

 Posterior semicircular canal. 

 Ductus fenestrae ovalis. 

 Ductus perilymphaticus. 

 Saccus perilymphatious. 

 Lagena cochlea. 

 Macula sacculia. 



pb 

 pa- 

 per' 

 rii. 



.spl 



Pars basilaris cochleae. 



Wider part of i)erilymphatic space. 



Narrower part of perilymphatic space. 



Ramus anterior. 



Ramulus neglectus. 



Ramus posterior. 



Ramulus sacculi. 



Saccule. 



Saccus fenestrae ovaUs. 



Saccus perilymphaticus. 



Tegmentum v;isculosum. 



Utricle. 



this membrane numerous irregular bundles of fibres, in the form of 

 trabeculae, pass into the space and form a rich network, wliich is 

 attached internally to the outer surface of the membranous labyrinth 

 and holds it in position. Free nucleated leucocytes are occasionally 

 m.et with in the meshes of this network. The perilymphatic sj)ace 

 is prolonged into two subsidiary cavities : — 



(i) The ductus fenestra ovalis (Retzius), (Fig. 245 '(fo) com- 

 mences as an opening {(n^f) immediately opposite the forariten ovale 

 of the hard capsule, which leads into a moderately large canal, the 

 structure under consideration. It passes forwards and outwards 

 through t\\e fenesira ovalu between the interstapedial and the outer 

 wall of the capsule into the oval depression [fossa fenestrae ovalis), 



