i 7 6 



THE QUARTERLY REVIEW OF BIOLOGY 



and their external reduplications extend 

 forward to the level of the antorbital 

 notches and thus entirely conceal the 

 palatine and alisphenoid bones, the open- 

 ing for the infraorbital canal is within 

 the temporal fossa, the zygomatic process 

 is placed far forward and its extremity is 

 in contact with the supraorbital process 

 of the frontal, the antero-posterior diam- 

 eter of the latter has been shortened and 

 the process as a whole deflected obliquely 

 forward as would be expected to result 

 from a lowering of the rostrum, and the 

 lachrymal bone has been pushed inward 

 and mortised into the maxillary instead of 

 being inserted between the maxillary and 

 the supraorbital process of the frontal. 



PHYSETERIDAE 



The most singular sort of odontocete 

 development is found in the physeteroid 

 porpoises, which begin their career, so 

 far as known, in the Lower Miocene with 

 skulls that possess all the structural details 

 of their successors in later geological 

 stages. It is confidently believed that 

 these somewhat generalized sperm whales 

 had been differentiated from the main 

 odontocete stock subsequent to the 

 elimination of the postorbital constric- 

 tion, but at a time long before the begin- 

 ning of the Miocene, and that many of the 

 diverse types that flourished in later 

 Miocene seas trace their ancestry back 

 to as yet unknown types of extinct 

 physeteroids. The living sperm whale 

 (Physeter catodon) has an enormous reservoir 

 on the top of the head, surrounded by a 

 fibrous integument, and divided interiorly 

 into compartments, which communicate 

 with one another and with cells or sinuses 

 also filled with liquid oil or spermaceti. 

 Beneath this reservoir, which may contain 

 10 to 15 barrels of liquid oil, is a great 

 mass of fibrous cellular tissue, likewise 

 saturated with spermaceti, known as the 



adipose cushion. Spermaceti, however, is 

 not always present, for occasionally cacha- 

 lots are killed that are "dry." If any 

 reliance may be placed on analogous 

 structural conditions in the living sperm 

 whale the structural details of these 

 early physeteroid skulls had been adjusted 

 to lodge a developing fat or spermaceti 

 cushion. Even in the Lower Miocene 

 Diaphorocetus the adipose cushion had 

 grown around the right side of the narial 

 passage, and as a result of this peculiar 

 condition the relative proportions and 

 relations of the bones forming the dorsal 

 surface of the skull had been altered in a 

 strange manner, producing a huge supra- 

 cranial basin, which was bounded behind 

 by the supraoccipital and laterally by the 

 elevated borders of the maxillaries. Most 

 peculiar of all these modifications is the 

 posterior expansion of the up-curved 

 right premaxillary bone which over- 

 spreads the anterior wall of the ' 'dished-in" 

 braincase. The vertex has been entirely 

 eliminated, the frontal bones are depressed 

 along the median line, one of the nasal 

 bones has been either lost or greatly 

 reduced and the other flattened against 

 the frontal behind the greatly enlarged 

 left narial passage, and the rostrum has 

 expanded laterally at the base. The 

 roof of the braincase seems to have been 

 depressed below its original level because 

 of the additional weight and pressure of 

 the developing adipose cushion. 



The oldest known Miocene physeteroids 

 as well as some of the later ones have 

 teeth implanted in distinct alveoli in the 

 maxillary and premaxillary bones. The 

 premaxillaries form the extremity of the 

 rostrum, and three teeth are implanted in 

 each bone. In the course of geological 

 time we observe that there is a tendency 

 among certain types for the teeth to 

 become loosely implanted in rather large 

 alveoli, and this condition is accompanied 



