ix. J PAL^ONTOLOG Y AND E VOL UTION. 189 



as such, the number of such forms has steadily increased 

 among the higher Mammalia. Not only do we now 

 know numerous intercalary forms of Ungulata, but M. 

 Gaudry's great monograph upon the fossils of Pikermi 

 (which strikes me as one of the most perfect pieces of 

 palseontological work I have seen for a long time) shows 

 us, among the Primates, Mesopiihecus as an intercalary 

 form between the Semnopitheci and the Macaci ; and 

 among the Carnivora, Hycenictis and Ictitherium as 

 intercalary, or, perhaps, linear types between the Viver- 

 ridce and the Hycenidce. 



Hardly any order of the higher Mammalia stands so 

 apparently separate and isolated from the rest as that 

 of the Cetacea ; though a careful consideration of the 

 structure of the pinnipede Carnivora, or Seals, shows, 

 in them, many an approximation towards the still more 

 completely marine mammals. The extinct Zeuglodon, 

 however, presents us with an intercalary form between 

 the type of the Seals and that of the Whales. The 

 skull of this great Eocene sea-monster, in fact, shows 

 by the narrow and prolonged interorbital region ; the 

 extensive union of the parietal bones in a sagittal suture; 

 the well-developed nasal bones ; the distinct and large 

 incisors implanted in premaxillary bones, which take a 

 full share in bounding the fore part of the gape ; the 

 two-fanged molar teeth with triangular and serrated 

 crowns, not exceeding five on each side in each jaw ; 

 and the existence of a deciduous dentition its close 

 relation with the Seals. While, on the other hand, the 

 produced rostral form of the snout, the long symphysis, 

 and the low coronary process of the mandible are ap- 

 proximations to the cetacean form of those parts. 



The scapula resembles that of the cetacean Hyperoodon, 

 but the supra-spinous fossa is larger and more seal-like ; 

 as is the humerus, which differs from that of the Cetacea 



