228 



NATURE 



{July s, 1883 



Platanista be really an exception) a pair of slender bones 

 are found suspended a short distance below the vertebral 

 column, but not attached to it, about the part where the 

 body and the tail join. In museum skeletons these bones 

 are often not seen, as, unless special care has been taken 

 in the preparation, they are apt to get lost. They are, 

 however, of much importance and interest, as their rela- 

 tions to surrounding parts show that they are the rudi- 

 mentary representatives of the pelvic or hip bones, 

 which in other mammals play such an important part in 

 connecting the hind-limbs with the rest of the skeleton. 

 The pelvic arch is thus almost universally present, but of 

 the limb proper there is, as far as is yet known, not a 

 vestige in any of the large group of toothed whales, not 

 even in the great Cachalot or Sperm Whale, although it 

 should be mentioned that it has never been looked for in 

 that animal with any sort of care. With regard to the 

 Whalebone Whales, at least to some of the species, the 

 case is different. In these animals there are found, at- 

 tached to the outer and lower side of the pelvic bone, 

 other elements, bony or only cartilaginous as the case may 

 be, clearly representing rudiments of the first and in some 

 cases the second segment of the limb, the thigh or femur, 

 and the leg or tibia. In the small Balcenoptera rostrata a 

 few thin fragments of cartilage, embedded in fibrous tissue 

 attached to the side of the pelvic bone, constitute the 

 most rudimentary possible condition of a hind-limb, and 

 could not be recognised as such but for their analogy 

 with 'other allied cases. In the large Rorqual, Balctnnp- 

 tera musculus, 67 feet long, previously spoken of, I 

 was fortunate enough in 1865 to find attached by 

 fibrous tissue to the side of the pelvic bone (which 

 was sixteen inches in length) a distinct femur, con- 

 sisting of a nodule of cartilage of a slightly compressed, 

 irregularly oval form, and not quite one inch and a half 

 in length. Other specimens of the same animal dissected 

 by Van Beneden and Prof. Struthers have shown the 

 same ; in one case, pirtial ossification had taken place, 

 tn the genus Megafitera a similar femur has been de- 

 scribed by Eschricht ; and the observations of Rein- 

 hardt have shown that the Greenland Right Whale 

 (Balana mysticetus) has not only a representative of 

 1 he femur developed far more completely than in the 

 Rorqual, being from six to eight inches in length and 

 completely ossified, but also a second smaller and more 

 irregularly formed bone, representing the tibia. Our 

 knowledge of these parts in this species has recently been 

 greatly extended by the researches of Dr. Struthers of 

 Aberdeen, who has published in the Journal of Anatomy 

 for 1881 a most careful and detailed account of the dissec- 

 tion of several specimens, showing the amount of variation 

 to which these bones (as with most rudimentary structures) 

 are liable in different individuals, and describing for the 

 first time their distinct articulation one with the other by 

 synovial joints and capsular ligaments, and also the most 

 remarkable and unlooked-for presence of muscles passing 

 from one bone to the other, representing the adductors 

 and flexors of mammals with completely developed limbs, 

 but so situated that it is almost impossible to conceive that 

 1 hey can be of any use ; the whole limb, such as it is, being 

 buried deep below the surface, where any movement, 

 except of the most limited kind, must be impossible. 

 Indeed, that the movement is very limited and of no par- 

 ticular importance to the animal was shown by the fact 

 that in two out of eleven whales dissected the hip-joint was 

 firmly anchylosed (or fixed by bony union) though without 

 •iny trace of disease. In the words of Dr. Struthers, " No- 

 thing can be imagined more useless to the animal than 

 rudiments of hind-legs entirely buried beneath the skin 

 of a whale, so that one is inclined to suspect that these 

 structures must admit of some other interpretation. Yet, 

 approaching the inquiry with the most sceptical determin- 

 ation, one cannot help being convinced, as the dissection 

 goes on, that these rudiments really are femur and tibia. 



The functional point of view fails to account for their 

 presence. Altogether they present for contemplation a 

 most interesting instance of those significant parts, rudi- 

 mentary structures." 



We have here a case in which it is not difficult to 

 answer the question before alluded to, often asked with 

 regard to rudimentary parts, Are they disappearing or 

 are tbey incipient organs ? We can have no hesitation 

 in saying that they are the former. All we know of the 

 origin of limbs shows that they commence as outgrowths 

 upon the surface of the body, and that the first-formed 

 portions are the most distal segments. The limb, as 

 proved by its permanent state in the lowest Vertebrates, 

 and by its embryological condition in higher forms, is at 

 first a mere projection or outward fold of the skin, which, 

 in the course of development, as it becomes of use in 

 moving or supporting the animal, acquires the internal 

 framework which strengthens it and perfects its functions. 

 It would be impossible, on any theory of causation yet 

 known, to conceive of a limb gradually developed from 

 within outwards. On the other hand, its disappearance 

 would naturally take place in the opposite direction ; pro- 

 jecting parts which had become useless, being in the way, 

 would, like all the other prominences on the surface of 

 the whales, hair, ears, &c, be removed, while the most 

 internal, offering far less interference with successful 

 carrying on the purposes of life, would be the last to 

 disappear, lingering, as in the case of the Greenland 

 Whale, long enough to reveal their wonderful history to 

 the anatomist who has been fortunate enough to possess 

 the skill and the insight to interpret it. 



Time will not allow of more illustrations drawn from 

 the structure of existing Cetacea ; we turn next to what 

 the researches of palaeontology teach of the past history 

 of the order. Unfortunately this does not at present 

 amount to very much. As is the case with nearly all 

 other orders of mammals, we know nothing of their con- 

 dition, if they existed, in the mesozoic age. Even in the 

 cretaceous seas, the def osits at the bottom of which are 

 so well adapted to preserve the remains of the creatures 

 which swam in them, not a fragment of any whale or 

 whale-like animal has been found. The earliest Ceta- 

 ceans 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, was intermediate between that of the 

 existing suborders of whales, having the elongated nasal 

 bones and anterior position of the nostrils of the Mystaco- 

 cetes, with the teeth of the Odontocetes, and with some 

 characters more like those of the generalised mam- 

 malian type, than of any of the existing forms. In fact 

 Zeuglodon is precisely what we might have expected 

 a priori 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 pri- 

 mitive 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 compressed 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 followed by five teeth with two distinct roots and 

 compressed pointed crowns, with denticulated cutting 

 edges. II 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 satisfactory. 

 Unfortunately the structure of the limbs is most imper- 

 fectly known. A mutilated humerus has given rise to 

 many conjectures ; to some anatomists it appears to indi- 

 cate freedom of motion at the elbow-joint, while to others 

 its characters seem to be those of the ordinary Cetacea. 



