492 SCHULTE, SEI WHALE. 



THE EAR. 



BY JOHN D. KERNAN, JR. 

 (Plate LVII, fig. 3). 



External auditory meatus: The external orifice of the auditory meatus is a minute opening 

 situated 24 mm. caudal to the center of the eye and 9 mm. dorsal. No auricular cartilage could 

 be found on gross examination, which alone was possible, nor were the muscles described by 

 Hanke 1 definitely ascertained to be present. 



The auditory meatus itself passes rostro-mesad in a groove in the squamosum, as described 

 by various authors. In the lateral part of its course it is an exceedingly small tube. Mesally 

 it expands like the mouth of a speaking trumpet and the ental extremity is attached to the 

 concave edge of the tympanum, and to that part of the squamosum which completes the tym- 

 panic ring. The lumen of the meatus is laterally circular. The mesal expansion takes place 

 in a horizontal axis, caudo-rostrad, and scarcely at all vertically. Thus the inner extremity of 

 the tube presents on cross section the appearance of a horizontal slit with dorsal and ventral 

 walls almost in contact. The plug of cerumenous material described by Lillie 2 and Hanke, 

 was not present. 



The membrana tympani is elliptical with the long axis pointing rostro-mesad, thus con- 

 tinuing the direction of the auditory meatus. The plane of the membrane is horizontal, so that 

 in place of forming an inner wall for the meatal canal, such as is found ordinarily in mammals, 

 the membrana forms in reality part of the roof. The inner extremity of the canal is formed by 

 the meeting of the dorsal and ventral walls at their joint attachment to the concave edge of the os 

 tympanicum. The extreme horizontal position of the membrana agrees with the basal position 

 of the whole auditory apparatus as found in Balcenoptera (van Kampen). 3 The circumference 

 of the membrana is attached to the sharp, concave outer margin of the os tympanicum, and to 

 the squamosum where the circle of the tympanic is incomplete. No distinction can be drawn 

 between pars tensa and pars flaccida. 



From the description of the membrana tympani thus far given it will be seen that at this 

 stage it is typically mammalian, that is a thin, oval membrane, slightly concave toward the 

 inner surface, attached by its margin to the tympanic ring. There is as yet no evidence of the 

 finger-like projection of the membrane outward into the lumen of the external meatus found in 

 the adult (Beauregard) 4 nor even any indication of its approaching formation as found by 

 Hanke in a somewhat older fcetus of B. musculus. 



In one important respect the membrane differs from that of other mammals; namely, 

 in its relation to the malleus. From this structure it is separated by a considerable space, the 

 membrane forming part of the ventral wall, the malleus lying close to the dorsal wall of the 

 tympanic cavity. The space between the two, which is triangular, is occupied by a fold of 

 tissue formed from the membrane itself. From the tip of the manubrium mallei to the inner 



1 Hanke, H. Ein Beitriige zur Kenntnis der Anatomie des ailsseren und mittleren Ohres der Bartenwall. Jenaische Zeitschrift 

 fur Xatur Wissenschaft, 1914. 



2 Lillie. On the Anatomy and Biology of the larger Cetacea. Proc. Zool. Soc. London, Vol. II, 1910. 



3 v. Kampen, P. N. Die Tympanalgegend des Saugetierschadels. Morph. Jahrb., Bd. XXXIV, Hefte 3 u. 4, 1905. 



4 Beauregard, H. Recherches sur 1'Appareil Auditif chez les Mammiferes. Jour, de 1'Anat. et de la Phys., An. 29-30, 1893-4. 



