NO. 8 INTERRELATIONSHIPS OF THE CETACEA WINGE 7 



The water acts in a very special way where the whale lets it stream 

 into the mouth for the purpose of catching the small animals which 

 it carries in with it. In such cases it brings about huge increase in the 

 size of the jaws together with many other remarkable peculiarities. 



For smelling there comes to be no use ; this sense is not exercised, 

 and the nose is therefore formed in accordance with the needs of 

 breathing only. The ethmoid degenerates. The numerous folded 

 laminje of which it originally consisted disappear, while the cribriform 

 plate loses its nerve perforations and becomes a solid lamina of bone 

 on the front wall of the braincase. The nose becomes a simple 

 passage for air. The air, which is exposed to strongly varying 

 pressure and temperature, has a tendency to provide itself with 

 greater space by widening out the nasal passage and Eustachian tube 

 wherever it meets with least resistance. It may form air-sacs, partly 

 on the upper side of the skull over the facial bones, partly on the 

 under side behind the palate. Here an air-sac may spread itself 

 forward along the outer side of the pterygoid and palatine and back- 

 ward along the outer margins of the body of the sphenoid and the 

 basal part of the occipital, pushing itself out under the ala parva, ala 

 magna and the squamosal, and bounded more or less by plate-like 

 outgrowths from all the bones mentioned. The bony palate is 

 lengthened backward still more by the pushing out from the ptery- 

 goids of laminae which extend into the soft palate beneath the nasal 

 passages. This clearly takes place partly under the action of the 

 tongue, but doubtless still more under the influence of the larynx. 

 The fact that the two original outer nostrils finally coalesce into one 

 is an indication of the nose's degeneration. 



■ The lacrimal bone is reduced and eliminated, or it fuses with 

 the cheek bone as in many other aquatic mammals, probably because 

 the bone is no longer acted upon by a lacrimal duct. 



The outer ear disappears from lack of use; the outer auditory 

 aperture is so strongly contracted that it may be difficult to find. 

 The bones of the inner ear acquire a peculiarity which is found 

 again in several other mammals that live in the sea, and which cer- 

 tainly in some manner or other must be dependent on aquatic life. 

 They are formed of unusually thick, stony-hard masses of bone ; this 

 is especially remarkable as regards the tympanic, the inner wall of 

 which is thickened in a peculiar way.' 



The dentition degenerates because the chewing of food is given up 

 as not easy to carry on satisfactorily under water. Most animals 

 chew with open mouth ; under water the chewed food would be 



