THE QUARTERLY REVIEW OF BIOLOGY 



an enormous size, and in correlation with 

 this increase the bones comprising the 

 rostrum have expanded horizontally. In 

 life the disproportionately large head 

 abruptly truncated in front, small eyes 

 placed near the angle of the mouth, and 

 blowhole on the edge of the muzzle, in 

 conjunction with a dorsal hump give 

 Phjseter catodon a very unusual appearance. 

 Skulls of adults measure 16 feet or more in 

 length and have a continuous maxillary 

 alveolar groove without any indication of 

 septa. The large palatine bones do not 

 form any part of the backward sloping 

 narial passages - , and are overridden 

 posteriorly and mesially by the pterygoid 

 bones. As many as 2.J teeth are lodged in 

 each mandible, and the symphysis is 

 equivalent to half of either ramus. The 

 posterior margin of the supracranial 

 depression is more abruptly elevated in the 

 physeteroids than in any other family of 

 cetaceans, and the basin extends farther 

 forward. In general the physeteroid skull 

 may be defined as having the rostrum 

 longer than the cranium, no sagittal 

 crest, rise of anterior border of lateral 

 wall of supracranial basin within the 

 antorbital notch, small lachrymals, elon- 

 gated jugals with styliform processes, 

 expanded palatines, small pterygoids, 

 and large foramina, which connect with 

 the infraorbital system. 



It is not improbable that, when more 

 is known of the immediate predecessors 

 of the living odontocetes, the diminutive 

 living Kogia breviceps will be found an 

 offshoot of some early Tertiary physe- 

 teroid . At present we have no knowledge 

 of their previous geological history. 

 Compared with a sixty-foot cachalot, an 

 eleven-foot pigmy sperm whale seems 

 rather small. It has an attenuated snout, 

 eyes placed nearer to the forehead, blow- 



holes on the forehead, and a falcate 

 dorsal fin. The skull of this porpoise is 

 characterized by a short rostrum, a well 

 defined sagittal crest, rise of anterior 

 border of lateral crest of supracranial 

 basin outside of antorbital notches, large 

 thickened lachrymal fused with styliform 

 jugal, small palatines, expanded ptery- 

 goids, and small foramina connected with 

 the infraorbital system. The mandible 

 has a short symphysis and is furnished 

 with 14 or 15 teeth. 



POSSIBLE ANCESTORS OF THE MYSTICETI 



The least modified cetacean skull thus far 

 collected is represented by Archaeodelphis 

 patrius (Allen, 19x1), whose critical pecu- 

 liarities of detail agree more closely with 

 mysticete than with odontocete cianial 

 construction. Annectant types are lack- 

 ing to connect Archaeodelphis with any 

 known cetothere, and the details herein- 

 after mentioned should not be interpreted 

 as implying that this Eocene cetacean 

 was the source to which cetotheres of 

 later geological stages owed their origin. 

 The most that can be said is that Archae- 

 odelphis and the cetotheres are derivatives 

 of the same common stock. 



Structurally this skull is much less 

 modified than any known fossil or living 

 whalebone whale. Obvious peculiarities 

 of the Archaeodelphis skull are the large 

 orbit, elongate flattened nasals and extrem- 

 ities of premaxillaries situated almost 

 entirely anterior to the supraorbital proc- 

 esses of the frontals, long and forward 

 sloping narial passages with distinct 

 dorsal nasal cavities, broad intertemporal 

 region, a triangular lachrymal extending 

 laterally as far as or beyond the maxillary 

 and overspread by the latter, and a 

 maxillary with infraorbital and ascending 

 processes. The position of the maxillary 

 with respect to the lachrymal, the orbit, 

 and the supraorbital process of the frontal 



