1010.] The Cetacca: Relations with the Zeuglodonts. 417 



bridge over the gap between the Zeuglodontia and Odontoeeti) is decidedly 

 of the longer, or Zeuglodont type and that therefore the supposed connection 

 of Zeuglodonts and Odontocetes breaks down at this point. He is inclined 

 to agree with Gill (1873) that the Cetacea are an extremely ancient branch 

 of the mammalian stem which cannot be connected with any known group 

 of land animals. Coming from an eminent cetologist, this conclusion will be 

 likely to carry great weight, l)ut a quite different interpretation of the facts 

 seems permissible. It is of course not at all necessary to suppose that any 

 known Zeuglodont is directly ancestral to Squalodon and the Odontocetes. 

 Indeed, the relatively large size and comparatively late appearance of all 

 known Zeuglodonts raises a strong presum[)tion against that idea; but the 

 hypothesis that the known Zeuglodonts are rather closely allied to the 

 ancestors of the Odontocetes and that these ancestors when discovered will 

 fall under a properly constructed definition of the suborder Zeuglodontia 

 has much evidence in its favor. 



Morphologically the Zeuglodonts realize many conditions which may 

 confidently be looked for in the ancestors of the Odontocetes. The earliest 

 Odontocetes must certainly have had an elongate premaxillo-maxillary 

 rostrum, retracted symmetrical nasals, a skull top sloping anteriorly, strong 

 post-orbital constriction, jjrominent post-orbital processes, small orbits 

 placed very low on the side of the face, slender jugals, a backwardly produced 

 palate in which the pterygoids shared, inflated petro-tympanic, condyles less 

 sessile and nearer to the median line, coronoid process of jaw broad not 

 hooked, condyle of jaw placed below level of cheek teeth, etc. With respect 

 also to the form of the limb bones, the Zeuglodonts are morphologically 

 intermediate between the Odontocetes on the one hand and normal placental 

 unguiculated quadrupeds on the other. The Zeuglodont humerus shoAvs, 

 it is said, a curious mingling of Pinniped with Cetacean characters (Lucas, 

 1895), but this neither proves that the Zeuglodonts are related to the Pinni- 

 peds nor casts any just suspicion upon their relationships with the Cetacea, 

 since the latter is probable on other grounds. A very striking fact is that the 

 scapula of Zeuglodon is of the Cetoid type (Lucas, 1895) in which the pre- 

 spinous fossa is rudimentary or absent, the acromion very large and situated 

 on the anterior border, and the coracoid prominent. Neither in the Pinni- 

 pedia nor in the Sirenia has adaptation to aquatic habits produced this 

 peculiar type of scapula, which is common to the Zeuglodonts and to the 

 Cetaceans. 



The brain cast of Zeuglodon, according to Elliot Smith (1903, pp. 322) 

 reveals no features that are inconsistent with Cetacean affinities, but it 

 resembles the Cetacean type in two important characters, namely, the great 

 breadth of the cerebrum, and the peculiar elongation of the olfactory pe- 

 duncles beyond the anterior extremities of the hemispheres. , 



