254 H. S. Harrison, 



2. Of these spaces, the spatium sacculare lies chiefly between 

 the membrane of the fenestra vestibuli (ovalis) and the sacculus; the 

 recessus partis neglectae lies below the pars negiecta; and the recessus 

 partis hasilaris below and in front of the pars basilaris. The three 

 are in communication by means of the ductus perilymphaticus, which 

 runs through the foramen perilymphaticum to join a fourth space, the 

 spatium meningeale, lying within the cavum cranii. The system of 

 spaces is closed, and is lined, in part at least, by an endothelium. 



3. The greater part of the wall of the membranous labyrinth is 

 thickened by a layer of specialized dense perilymphatic tissue ("Spindel- 

 knorpel"). Over the three areas of contact with the perilymphatic 

 system, this layer is absent, and the perilymph and endolymph are 

 separated hy a thin membrane consisting of flattened ectodermal cells 

 of the labyrinth luall and endothelial cells of the perilymphatic spaces. 

 The membrane in each case is attached at its periphery to more rigid 

 parts of the labyrinth wall, which thus forms a supporting frame 

 ("Knorpelrahmen"). The tympanal area is in each case opposite to a 

 macula acustica. Vibrations of the membrane of the fenestra vestibuli 

 must be transmitted through the perilymph, first of all to the tympanal 

 area of the sacculus, then along the ductus perilymphaticus to the 

 tympanal areas of the pars negiecta and pars basilaris, and are pro- 

 bably lost in the spatium meningeale. The pars superior of the laby- 

 rinth has no direct relations with the perilymphatic system. 



4. The chief differences between Urodela and Anura as regards 

 the perilymphatic system proceed from the increase in the size and 

 importance of the recessus partis basilaris in the latter group. It 

 acquires an independent aperture to the exterior (the foramen peri- 

 lymphaticum inferius) and passes out to form the saccus perilympha- 

 ticus, which lies at the anterior end of the fissura metotica (foramen 

 jugulare). 



Ò. The connection between recessus partis basilaris and ductus 

 perilymphaticus is in the Anura drawn out into a short duct, the duc- 

 tus reuniens. In Pelobates fuscus, before metamorphosis, this portion 

 lies within the auditory capsule, thus closely resembling the condition 



