48 



PROCEEDIKUS OF THE ACADEMY OP 



[1894. 



the reptile or in the higher vertebrata. In some respects it is a 

 peculiarly ichthyic bone though not invariably present even within 

 the limits of the class, as already mentioned. 



The ear-chamber in reptiles is more or less closed, internally at 

 least, in the adult condition by three bones separated by a Y-shaped 

 suture distinctly visible in the longitudinally divided skull (Fig. 9). 

 The two lower. No. 2, 6, (Fig. 9,) of the three bones are situated 

 on either side of the vertical stem of the Y-shaped suture, the third 

 remaining bone No. 3 within the diverging branches of the latter. 

 Externally the osseous vestibule presents a fenestra rotunda fnr 

 (Fig. 11), situated entirely within the bone No. 2 and a fenestra ovalis, 

 fno, the posterior half of which is formed by the margin of the bone just 

 mentioned, the anterior half by that of the bone No. 6. The mem- 

 branous labyrinth consists of a vestibule, semicircular caual and, in 

 the turtle and alligator, of a rudimentary cochlea. The fenestne are 

 closed by membranes in the living animal and to that of the fenestra 



p ovalis is attached a col- 



/J umellar-like bone which, 



on account of being con- 

 nected with the mem- 

 brana tympani, is re- 

 garded as the homologue 

 of the stapes of the hu- 

 man ear. The membra- 

 na tympani is attach- 

 ed in turn to bone 

 No. 28, (Figs. 7, 10) 

 usually called the quad- 

 rate and regarded as 

 representing either the tympanic bone or the malleus in Man.^'^ 



The tympanic membrane being so superficially situated, neither 

 external auditory meatus nor external ear can be said to exist in 

 reptiles. The nearest appi'oach to an external ear is seen in the 

 ci'ocodilia which are provided with two cutaneous folds situated just 



117" 

 2. 



Fig. 11. 



External view of auditory region of 

 alligator. 



■'■' Some of the reasons that may be regarded in favor of accepting the latter 

 hypothesis as the correct one have already been stated. 



