NO. 8 INTERRELATIONSHIPS OF THE CETACEA WINCE 1/ 



taceans, or other small creatures, which they allow to stream into the 

 mouth in multitudes along with the water. They seek to retain the 

 edible contents when they close the mouth and the water flows out 

 again between the lips. The water has thereby accjuired great power 

 to act upon the mouth cavity from within ; it distends the opening 

 enormously ; the jaws grow and acquire a disproportionately large 

 size in comparison with the braincase ; the branches of the mandible 

 are bowed strongly outward to the sides and are widely divergent 

 from each other behind, while the connection between them in front 

 becomes quite loose. The gigantic lower jaw wears so upon the 

 ligaments which bind its articular head to the squamosal that the 

 ligaments are incited to growth. They become uncommonly strong 

 and spread themselves over the original gristle-covered articular 

 surfaces on the jaw and the squamosal, both of which surfaces they 

 entirely cover. They cause the squamosal to grow out as a huge 

 process which bears the attachment surface for the lower jaw on its 

 free margin. By the enlargement of the mouth cavity the squamosal 

 together with the articular head of the lower jaw is pushed far out 

 to the side and so far back that at last its free postero-external 

 extremity comes to lie further back than the occipital condyles. The 

 squamosal in its turn presses strongly on the parts which lie behind 

 it : on the mastoid which is squeezed inward, and on the exoccipital 

 which is pushed backward. In proportion to the size of the under 

 jaw the temporal muscle increases and pushes its region of origin 

 forward over the supraorbital process. There has been no use what- 

 ever for the teeth ; they atrophy so completely that finally they are to 

 be found only in the embryo as a long series of insignificant, small, 

 pin-shaped teeth, hidden under the skin and soon resorbed. On the 

 other hand the inflowing and outflowing water acted as a stimulant 

 on the corneous papillae of the roof of the mouth. The papillae along 

 the margin of the upper jaw are so stimulated that they have grown 

 out as a close-set series of " whale-bones " : high, crosswise-placed, 

 corneous plates, the inner margin of which is frayed out into threads. 

 The entire set of whale-bones functions as an excellent instrument 

 for catching the solid material that flows with the water into the 

 open mouth. The palate is strongly acted upon by the instreaming 

 water, by the larynx, and by the tongue, which is pressed against it 

 when the water is to be expelled. The palatine bone grows and forces 

 itself backward, pushing back the pterygoid behind it ; and the 

 pterygoid pushes and presses that which lies still further back ; 

 namely, the tympanic bulla and the region of attachment of the neck 



