NO. 8 INTERRELATIONSHIPS OF THE CETACEA WINGE 39 



In all other Xiphiines the zygomatic process of the squamosal is 

 smaller and more atrophied, the teeth in the upper jaw disappear, 

 while of those in the lower jaw one or two only remain in each ramus 

 and these are particularly modified. A peculiarity of at least the 

 living forms of the section is the unusual size of the air-sac at the 

 outer side of the pterygoid, which is shaped to fit it. Somewhat of a 

 peculiarity likewise is partly the height of the spinous processes on 

 the dorsal and caudal vertebrae (while the transverse processes are 

 relatively rather short), and partly the small size of the hand. The 

 former character indicates unusually heavy dorsal and caudal muscles, 

 or perhaps a widening out of the muscles in a different direction — 

 more upward than sideways — than in the Delphinids with specially 

 long transverse processes. The latter makes it appear that the hand 

 is somewhat disused. The cervical vertebrae are inclined to coalesce 

 as in the Physeterines. 



In the members of the group Xiphii, as contrasted with the 

 Hyperoodontes, the bones of the face have remained primitive to the 

 extent that no raised longitudinal crest is present on the maxillary in 

 front of and above the orbit ; at most there is found in the correspond- 

 ing place a weak cushion-shaped elevation. But in other ways the 

 bones of the face have increased in strength and have permitted them- 

 selves to be moulded by the pressure of the water. 



In a few respects Mesoplodon is the most primitive among the 

 Xiphii. To be sure, the facial cushion, by pressing back against the 

 occipital wall, has caused the median part of the wall, formed for the 

 most part of projecting outgrowths of the intermaxillaries, to be 

 abruptly elevated. But- the cushion has not acted on the wall to such 

 a degree that the upper margin together with the nasal bones has been 

 either very strongly forced back or caused to bend forward in any 

 noteworthy manner ; neither has it formed for itself any distinct pit 

 around the nares. Moreover the intermaxillaries have retained their 

 original relation to the mesethmoid, which they do not grow over. 

 On the other hand the rostrum acquires increased strength by the 

 ossification, as age advances, of the mesethmoid, and its coalescence 

 with the surrounding bones into a stony-hard mass. Of the teeth in 

 the upper jaw there is found in Mesoplodon at most a series of quite 

 small remnants, more or less hidden in the skin and scarcely leaving 

 any traces in the bones. In the lower jaw there is found only one 

 well-developed tooth. This is situated at the front of the mandible 

 and is peculiarly modified, having a large, compressed crown and a 

 big root which sometimes, presumably in the male especially, may 



