1883.] on Whales, Past and Present^ and their Probable Origin. 373 



of whose organisation we have any good evidence, are the Zeuglodons 

 of the Eocene formations of North America. These were creatures 

 whose structure, as far as we know it, w^as intermediate betw^een that 

 of the existing suborders of whales, having the elongated nasal bones 

 and anterior position of the nostrils of the Mystacocetes, with the 

 teeth of the Odontocetes, and with some characters more like those of 

 the generalised mammalian type, than of any of the existing forms. 

 In fact Zeuglodon is precisely what we might have expected a piori 

 an ancestral form of whale to have been. The remarkable smallness 

 of its cerebral cavity, compared with the jaws and the rest of the 

 skull, so different from that of modern Cetaceans, is exactly paralleled 

 in the primitive types of other groups of mammals. The teeth are 

 markedly differentiated in different parts of the series. In the 

 anterior part of both jaws they are simple, conical, or slightly com- 

 pressed and sharp pointed. The first three of the upper jaw are 

 distinctly implanted in the premaxillary bone, and so may be reckoned 

 as incisors. The tooth which succeeds, or the canine, is also simple 

 and conical, but it does not greatly exceed the others in size. This 

 is follow^ed by five teeth with two distinct roots and compressed 

 pointed crowns, with denticulated cutting edges. It has been thought 

 that there was evidence of a vertical succession of the molar teeth, 

 as in diphyodont mammals, but the proof of this is not quite satis- 

 factory. Unfortunately the structui-e of the limbs is most imperfectly 

 known. A mutilated humerus has given rise to many conjectures ; to 

 some anatomists it appears to indicate freedom of motion at the 

 elbow-joint, while to others its characters seem to be those of the 

 ordinary Cetacea. Of the structure of the pelvis and hind-limb we 

 are at present in ignorance. 



From the middle Miocene period fossil Cetacea are abundant, and 

 distinctly divided into the two groups now existing. The Mysta- 

 cocetes, or Whalebone Whales, of the Miocene seas were, as far as we 

 know now, only BaloinoiAerce, some of which (as the genus Cetotheriiim) 

 were, in the elongated flattened form of the nasal bones, the greater 

 distance between the occipital and frontal bones at the toj) of the 

 head, and the greater length of the cervical vertebrae, more generalised 

 than any now existing. In the shape of the mandible also, Van 

 Beneden, to whose researches we are chiefly indebted for a knowledge 

 of these forms, discerns some ai^proximation to the Odontocetes. 

 Eight Whales (Balcena) have not been found earlier than the Pliocene 

 period, and it is interesting to note that instead of the individuals 

 diminishing in bulk as w^e approach the times we live in, as with 

 many other groups of animals, the contrary has been the case, no 

 known extinct species of whales equalling in size those that are now 

 to be met with in the ocean. The size of whales, as of all other 

 things whose most striking attribute is magnitude, has been greatly 

 exaggerated ; but when reduced to the limits of sober fact, the Green- 

 land Eight Whale of 50 feet long, the Sperm Whale of 60, and the 

 Great Northern Eorqual (Balcenoptera Sibbaldii) of 80, exceed all 



