Oll ilio Perilympliatic Spaces of the Ainpliibiini Ear. 261 



wards, below the pars neglecta and above the pars basilaris. (x 25). 

 Figs. 16—21 (x 50) illustrate the connection between ductus perilympha- 

 ticus and recessus partis basilaris, showing also the foramen perilympha- 

 ticum inferius (figs. 18, 19, 20). In fig. 19 the ductus reuniens is seen 

 half way between the auditory capsule and the cavum cranii, surroun- 

 ded by cartilage. Fig. 21 shows the fibrous strand connecting lung 

 and Saccus perilymphaticus {st). The sections form a series 1, 2, 4, 7, 

 9, 10, 15; thickness 0,03 mm. 



Fig. 22. Transverse section through auditory capsule of metamorphosed Pelobates 

 fuscus (40 mm long), showing ductus reuniens within cranial cavity 

 (cf. figs. 17—20). xSO. 



Fig. 23. Transverse section through auditory capsule of adult Rana temporaria. 

 to show spatium sacculare applied to the tympanal area of the sacculus. 



Fig. 24. Transverse section of auditory capsule of Rana fusca larva (21 mm), 

 showing recessiis partis basilaris at aai early stage, x 50. 



Figs. 25 — 28. Transverse sections of Rana fusca during metamorphosis (length 

 37 mm). In fig. 26 the ductus reuniens is seen to run in a groove in- 

 dicative of its secondary inclusion within the cranial cavity. Fig. 27 

 shows the foramen perilymph aticum accessorium, opening from the saccus 

 perilymphaticus into the cavum cranii. Cf. fig. 20, of Pelobates; by the 

 absorption of the bar of cartilage on the left of B.R, a condition similar 

 to that seen in fig. 27, would be attained. Fig. 27 shows also the fibrous 

 strand running from saccus perilymphaticus to tracheal chamber {st). 

 (Series 1, 6, 10, 14. Thickness 0,02 mm.) x 50. 



Fig. 29 — 35. Transverse sections of auditory capsule of larva of Bufo cinereus 

 (20 mm). Figs. 31 and 32 show connection between recessus partis 

 basilaris and ductus perilymphaticus. Fig. 35 shows the anterior end of 

 the fissura metotica. (Series 1, 4, 6, 8, 11, 12, 13. Thickness 0,02 mm.) 

 x50. 



Fig. 36. From transverse section of young Siredon pisciformis Section passing 

 through fenestra vestibuli, to show continuity of the membrane with the 

 perichondrium. X 70. 



