4 6 



THE QUARTERLY REVIEW OF BIOLOGY 



thin underlying lateral plate-like exten- 

 sion of the frontal, forms a roof more or 

 less complete over the temporal fossa. 

 As viewed from the side the long axes of 

 the frontal, parietal, and squamosal slope 

 upward and backward, and give every 

 appearance of having been crowded into 

 their present position by some backwardly 

 delivered force associated with the pos- 

 terior overthrust of the maxillary. These 

 opposite trends of thrust in the elements 

 chiefly concerned in the telescoping proc- 

 ess may be illustrated by the skulls of the 

 bottlenose porpoise (Tursiop truncatus) 

 and the Sei whale (Balaenopera borealis). 



Among the unusual conditions that have 

 .arisen through this telescoping process 

 are the contact of the premaxillary with 

 «he supraoccipital (Kogia), the overriding 

 of the palatine by the pterygoid and the 

 contact of the latter with the maxillary 

 (Platanista), the antero-posterior expan- 

 sion of the alisphenoid and its contact 

 with the supraoccipital (Aulophyseter), 

 the backward projection of the lachrymal 

 along the outer upper border of the supra- 

 orbital process of the frontal (Xenorophusj, 

 the outward extension of the facial por- 

 tion of the premaxillary beneath the 

 maxillary (Xettor&phus), the sutural union 

 of the external reduplication of the 

 pterygoid with the squamosal (Eurhinodel- 

 phis, Zarhachis, Platanista, and Stenodel- 

 phisj, the coalescence of the mesethmoid 

 and ectethmoids to form a flattened bony 

 plate on anterior wall of braincase over 

 the greatly reduced frontal fontanelle 

 (practically all living delphinoids), the 

 wing-like lateral extension of the vomer 

 which is applied to the ventral surface of 

 the maxillary (young Physetef), the loss 

 •of the right nasal bone (Physeter), and the 

 close approximation of the nasal bones 

 with the supraoccipital (Sibbaldus). In 

 the case of the blue whale (Sibbaldus 

 .musculus) portions of the nasal, premax- 



illary, maxillary, parietal, and frontal 

 are present in one transverse plane. Re- 

 arrangements of the individual bones 

 such as enumerated above are peculiar to 

 the cetaceans and are the direct outcome of 

 a remodeling of the skull. 



ODONTOCETI 



Small archaic toothed whales with 

 skulls constructed along somewhat differ- 

 ent lines from those of the zeuglodonts 

 make their appearance toward the close 

 of the Eocene. Their previous geological 

 record is as yet unknown. If they were 

 contemporaneous with the Middle Eocene 

 and earlier Upper Eocene zeuglodonts, it 

 seems surprising that their remains have 

 never been found or at least identified 

 among the many specimens obtained by 

 the various parties that have explored the 

 Fayum in Egypt. Other possibilities to 

 be taken into consideration are that these 

 archaic toothed whales may have been 

 developing in some other part of the world 

 or in fresh water, and that they first came 

 into association with the zeuglodonts on 

 the shores of the southern United States. 

 Skulls of two of these small whales differ- 

 ing from one another in certain details of 

 telescoping have been discovered in de- 

 posits approximately equivalent in time 

 to those in which our North American 

 Upper Eocene zeuglodonts were found. 

 The braincases of these skulls are short 

 and broad, quite compact, and less modi- 

 fied in some respects than in cetaceans 

 occurring in later epochs. As compared 

 with the zeuglodonts, they are noticeably 

 contracted in a fore-and-aft direction. 

 The individual bones in the skull as a rule 

 are more ponderous than in the lighter 

 constructed skulls of modernized por- 

 poises. 



These archaic toothed whales tried out 

 a number of cranial modifications and long 

 before their apparent extinction near the 



