771) Mn. D. G. LILLIE OX TUK ANATOMY | ^I"}' 2i, 



those purts of the iuulitory oigan, in Bahpuoptera rostrata, Avhicli 

 Avere described by Drs. Cu-te and Macalihter * in tlieir excellent 

 paper on the anatomy of a member of that species published in 

 1H()7. J)r. Dwiglitt has also described the bones of the auditory 

 organ of B. musculus at some length in a, paper published in 1872. 

 It will thus be only necessary l)rietiy to recapitulate here the 

 jiarts of the organ which are already known and to add some 

 ol)servations which appear to be new. 



The o}iening of the external auditory meatus on the siuface of 

 the heail is a relatively small slit situated at a short distance 

 behind the eye in a horizontal line with the connnissure of the 

 lips. There is no trace of a pinna. The auditory canal is con- 

 tiinied ])ackwards from this aperture until it reaches as far as the 

 zygomatic process of the squamosal bone where it turns inwards 

 and, increasing somewhat in diametei", proceeds along a groove in 

 the squaniosiil bone (text-tig. 71, Sq.^) which winds roinid the 

 posterior border of that bone to reach the tympnnic membrane. 

 The diameter of this tube townrds its innei' and wider extremity 

 was about one and a half indies in the two species under con- 

 sideration. 



The tympanic membrane (Fl. LXXIY. tig. 1) seems to have 

 esG^ped the notice of previous ol)sei'vers. It is highly modified and 

 is a siic-like structure not uidike the finger of a glove. The sac 

 (1^1. LXXIA'. tig. 1,/") is about three inches long and tln-ee-quarters 

 of an inch in diameter and tapers to a rounded point at the outer 

 or distal end. The walls of the sac are about one-tenth of an inch 

 in thickness, and consist chietiy of white fibrous tissue and yellow 

 elastic tissue. No nerve-cells or fibres and no muscle-fibres have 

 been foundup to the present. From the upper surface of the snc 

 in the median line a ligament about an inch long and 5 mm. in 

 diameter projects forwards towards the tymjianic cavity. The 

 ligament is continued along the sac in the opposite direction as a 

 ridge. The total length of the tympanic sac; and ligament is 

 al)oat four inches. The mouth of the sac opens into the tympanic 

 cavity, while the outer ])ortion pi'ojects into the external auditory 

 meatus. The inner extremity of the latter joins the rim of the 

 sac (PI. LXXIV. fig. 1, h). The ligamentous process passes under 

 the junction of the malleus and incus, and becomes attached at its 

 ])i-oximal end to the very much reduced manubi'ium of the malleus. 

 'J'he malleus is fused to the tympanic bone, as has been already 

 pointed out by Drs. Cai-te and Alacalister. Thus in Balanoptpra 

 the tympanic membrane has become a sac-like organ, which 

 projects outwards and is attached by a ligament to a rigid process 

 of the tympanic bone — this process being the malleus. 



In the external auditory meatus of all the individuals examined 

 at Innishkea there was a solid plug of wax-like sul).st<inceof fairly 

 definite size and shape which does not seem to have been hitherto 

 described. This plug (PI. 3-.XXIV. fig. '2) was usu.illy about 



* (':irtc .t Mnc;ili>lci-, Phil. Triiis. 18ti7, p. •-'.".2. 



t Dwi^rlit. MriiRiii> Iin!-t(iiiS,)i-. Nut. His.t. 187'.', vol. ii. p. '-'25. 



