NO. 5 TELESCOPING OF THE CETACEAN SKULL 9 



pi. 3, figs. 5, 6), provides adequate support for the rostral portion of 

 the maxillary. Its superficial area in a skull of DclpJiiniis (pi. 5, 

 fig. 4) is about equal to that of the rest of the bone, in one of Grampus 

 it is about twice as great ; while in a pike whale it is less than one- 

 twelfth.'' There is, furthermore, no orbital portion of the bone to 

 interfere with lowering the expanded postorbital process of the 

 frontal to any required level. Basining, therefore, as might be ex- 

 pected, is, in this group, carried to the extreme, culminating in the 

 conditions seen in the sperm whale (pi. 6, fig. i) and Kogia (pi. 7, 



fig. 3). 



In order to explain the origin of the two kinds of telescoping it 

 appears to be necessary to look for some other factor than the work 

 of difit'erent forces applied to the remodeling of one original type 

 of structure (see pp. 35-39). Special elements of a kind which 

 seemingly might have an important bearing on the initiation of two 

 such processes in the superficial portion of the skull have already 

 been shown (pp. 5-6) to exist among mammals that have not under- 

 gone cetacean modification. The skull of the fox and sea-lion re- 

 spectively, furnish combinations resembling those which might be 

 supposed to be required (pi. 2). Turning to the base of the dis- 

 articulated maxillary in the same two animals it immediately becomes 

 obvious that here once more are apparently the looked-f or conditions. 

 The maxillary of a sea-lion (pi. 3, fig. i), like that of a furseal (pi. 3, 

 fig. 2), when viewed from behind, is seen to have essentially the same 

 structure as that which has been found (pp. 7-8) to exist in the dis- 

 articulated maxillary of a baleen whale (pi. 3, fig. 3), while that of 

 a fox (pi. 3, fig. 4) might pass, by a series of relatively unimportant 

 changes, into that which is found (pp. 7-8) in the similarly treated 

 maxillary of a toothed cetacean (pi. 3, figs. 5 and 6). The essential 

 feature of difference between the proximal portion of the maxillary 

 of a northern sea-lion or a furseal and that of a fox is that in the 

 seal type the orbital part of the bone is developed outward beyond the 

 alveolar level as a broad horizontal plate (o. />/.) independent of the 

 tooth row, while in the fox type it is confined to the region directly 

 above the alveoli ; its entire base, in the fox, serves as a support to 

 the teeth, and its outer portion is tilted upward and outward at a 

 conspicuous angle. In the maxillaries of both animals the " malar 

 process " extends along the margin of the orbital plate from the 



* A further indication of the mechanical weakness of this part of the 

 mj'Sticete skull is the relatively great frequency with which weathered or 

 fossil specimens are found lacking the rostrum. 



