1910.] AXD BIOLOOV OF THE LARGER CETACHA. 781 



produced by tlie water on the external surface of the membrane 

 .as the animal dived would tend to compress the walls of the sac. 

 Tliere may be some means by which this increased pressure is 

 made known to the animal, and thus enable the curiously modified 

 tympanic membrane to serve as a pressure-gauge ; but it is not 

 possible to assign any function to the structure at present. 



The whale probably receives sound-vibrations by means of 

 vibrating bony surfaces, after the manner of fishes. The tympanic 

 bulla is a relatively dense and heavy soundiug-ljox, fastened to the 

 periotic bone by two thin pedicles, so that it could be easily set in 

 vibration. The bulla is counested with the fenestra ovalis by the 

 chain of ossicles, the auditory apparatus being thus independent 

 of the tympanic membrane, which may have some other function, 

 possibly that of a pi-essu re-gauge. 



The description of the ear of Bakcna mysticetas given by Home* 

 in 1823 seems to correspond to some extent with the above account 

 of that organ in Balreiioptera. The ear of the Odontocet.^s 

 appears to be more like that of ordinary Mammals t. 



V. The Asymmetry of the Odoxtocete Skull. 



It has long been recognized that a want of symmetry exists 

 in the Odontocete skull, centred round the nasal region ; l)ut 

 authorities seem still to be at a loss to account for this irre- 

 gularity. Mr. Beddard % sums up the difficulty thus : — " It is 

 easier to say that the asymmetr}'-, being, as it is, chiefly developeil 

 in the regions of the blow-holes, has something to do with these 

 structures, than to find any adequate reason for connecting the 

 two." From an examination of the skull alone an explana- 

 tion certainly doe^s not present itself very' readily. But when 

 the anatomy of the head and neck of a symmetrical Mysta- 

 cocete, such as BalamojJtera mihscidus Linnivus, is examined, 

 and the relations of all the parts studied and compared with those 

 of an asymmetrical Odontocete, such as Physeter macrocephalas 

 Linnteus, the ]iroblem becomes greatly simplified, and a solution 

 seems to ofier itself. 



In the Cetacen, the arytenoid and epiglottidean cartilages form 

 a long, ligid, cylindrical tube, a continuation of the larynx, which 

 rises up through the floor of the phaiynx like a pillar and is thrust 

 up between the alveolated walls of the nasopharyngeal chamber, 

 which form the roof of the pharynx in this region. In the larger 

 whales this pipe is about one foot in length. A somewhat similar 

 pipe-like epiglottis, connecting the larynx with the posterior nares 

 also occui'S in the Marsupials and Ungulates ; but it is less pi-o- 

 nounced than in the Cetncea. 



In the case of the symmetrical Mystacocetes this tulje is 



* Home, 'Lectures on Coinii;ir:ilive Anatomy' (1823), Vol. iii. Loc>t. I\., \'oI. iv. 

 Tal.s. 0. & ci. 



+ Hunter, Phil. Trans. 1787, p. WO. 

 X HeddHnl, ' A Hook of Whales,' p. 49. 



Pkoc. ZuoL. Sue. 1910, No. LI. 51 



