NO. 8 INTERRELATIONSHIPS OF THE CETACEA WINGE 29 



peculiarity, which in any event soon showed itself, is the reduction of 

 the temporal muscle through lack of use ; its fossa becomes smaller 

 and the zygomatic process of the squamosal becomes less projecting 

 and less robust, losing, moreover, its primitive arched form. In the 

 more advanced members of the family many other modifications may 

 appear. The facial part of the skull, which begins by being long and 

 narrow, almost compressed, used as forceps, may become still longer. 

 Or the use as forceps may grow less and be exchanged for service as 

 an implement for rooting in the sea bottom ; followed by alteration in 

 the form of the face. Or the mouth is used merely to clap together 

 around the prey ; followed by flattening and shortening of the face. 

 In each instance the facial cushion contributes to the flattening of the 

 facial part of the skull. The extreme tip of the intermaxillary has 

 the tendency to be restricted, to be grown over by the maxillary and 

 to lose the teeth which at first were implanted in it. Its upper margin 

 may extend in over the anterior part of the mesethmoid and coalesce 

 with its fellow of the opposite side. The symphysis menti has a 

 tendency to be weakened and shortened. The teeth are inclined to a 

 further reduction, and they may disappear; but they may also be 

 again applied to special work and be modified in various ways. The 

 braincase increases in size and is more subject to pressure from in 

 front and from behind. The nasal passage may be pushed further 

 back. The nasal bone, which in the most primitive Delphinids 

 retained a slight trace of its earlier function as a cover for the nasal 

 cavity, becomes in most cases quite sunk into the frontal. The 

 occipital condyle, which at first is rather projecting in the usual 

 manner, becomes flattened out and pressed in against the wall of the 

 braincase. The cervical vertebrae may coalesce. The thoracic verte- 

 bras acquire unusually long transverse processes which are especially 

 noticeable on the hindmost of the series. Most of them are dia- 

 pophyses except the most posterior ones ; these are parapophyses. 

 Only the anterior ribs retain the capitulum. On the hindmost ribs 

 the capitulum disappears entirely, and the rib is articulated with the 

 tip of the long transverse process by the tuberculum only. (As in the 

 Platanistids the single articular head on the very hindermost ribs is 

 presumably formed by the capitulum or by the capitulum and tuber- 

 culum undivided.) The flippers may be lengthened. Etc. The ptery- 

 goid varies capriciously. It is true that it always spreads inward 

 under the posterior nares ; but it is sometimes rather widely separated 

 from its fellow of the opposite side, sometimes almost in contact with 

 it, while probably after having been in the latter condition it may 



