ZEUGLODONTS 309 



The Archaeoceti are toothed whales ; but, whereas 

 in the Odontocetes the teeth are all alike (with merely 

 difference in size), the teeth of the present group are 

 like those of more typical mammals, in being dis- 

 tinctly separable into three series. There are three 

 incisors on each side of each jaw, and those of the 

 upper jaw are borne by the pre-maxillae, the bone which 

 bears the incisors in mammals generally ; behind the 

 junction of the pre-maxilla with the maxilla is a 

 definite canine, and behind this again five teeth, 

 which are no doubt both molars and pre-molars, 

 though there is no positive evidence of a double 

 dentition in the Zeuglodonts. It will be noted too 

 that the total number of teeth (thirty-six) is that of 

 many mammals. 



The skull is elongated like that of whales in 



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general ; and, as in other whales, the snout is long. 

 The frontal bones come down over the orbit as in all 

 whales ; but the nasals are long and, ordinarily, 

 mammalian. The result of this latter arrangement is 

 that the blow hole was in the middle of the snout 

 instead of at its base, as in all whales except Pkyseter, 

 where, it will be remembered, there is a canal 

 embedded in the soft tissues of the head leading to 

 the extremity of the snout. It is the whalebone 

 whales among living Cetacea which have best pre- 

 served the form of the nasal bones of Zeuglodon. 

 Other bones of the skull besides the nasals are not 

 upon the Cetacean plan. The pre-maxillae take a 

 large share, as has been already implied, in the 

 formation of the gape. The parietals, which in 



