The Cambridge Natural History Part 27

The pectoral fin of Whales exists in two forms. In the Toothed Whales it is shorter and rounder; in the Whalebone Whales longer and narrower.

Structural differences accompany these outward dissimilarities. In the first-named group the humerus and the beginning of the radius and ulna are within the body, and do not form a part of the fin. In the Whalebone Whales, on the other hand, the fin contains all the bones of the fore-limb.

Another remarkable contrast between the hand in the two groups of Whales is that while the Toothed Whales have five fingers, thus justifying the prevailing opinion that they are the more primitive of the two groups, the Whalebone Whales have only four fingers. Actually the Right Whale, _Balaena_, seems to have five fingers; and, indeed, the fact that it has, is often used to distinguish it from the Humpback, which has undoubtedly only four. But a careful consideration of the state of affairs which prevails in the foetus of _Balaenoptera_ dispels this idea. Between what are apparently the second and third fingers, a rudimentary finger, consisting of four phalanges, appears. This is not produced, as is an additional finger found in the White Whale or Beluga, by a splitting of a finger. Accordingly the four-fingered condition of the Whalebone Whales is produced by the dropping out of a finger in the middle of the series,--a very remarkable fact. When fingers disappear, as, for instance, in the Horse, etc., it is at the two ends of the series that the digits vanish. If this view of Professor Kukenthal's[230] be accepted, it follows that the presumed thumb of the Right Whale is what has been termed the prepollex.

The hand of the Whales, like those of some other aquatic creatures, _e.g._ the reptile _Ichthyosaurus_, has a larger number of phalanges than have terrestrial animals. The result of this is, of course, to increase the length of the fin and its utility as a paddle. It is commonly not all the fingers that have developed this great number of accessory phalanges.

Rudimentary nails have been found upon the Cetacean hand; but in no case are they functionally developed. In the Manatees we have the disappearance of the nails still imperfectly accomplished. In _M. latirostris_ there are nails; these have vanished, apart from possible traces to be seen with a microscope, in _M. inunguis_.

A very characteristic feature of certain Whales are the furrows {345} to be seen on the throat. This is especially the case with the Rorquals, in which group the Humpback Whale, _Megaptera_, is to be included. The whales of these two genera (_Balaenoptera_ and _Megaptera_) have a large number of the throat furrows--as many as sixty have been counted. Some other Whales have a smaller number; thus _Rhachianectes_ has but two on each side, and the Physeteridae have not many more. These furrows are absent in very young embryos. It is thought by Professor Kukenthal that they allow of a wide opening of the mouth.

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FIG. 181.--Dorsal surface of bones of right anterior limb of Round-headed Dolphin (_Globicephalus melas_). 1/10. The shaded portions of the digits are cartilaginous. _c_, Cuneiform; _H_, humerus; _l_, lunar; _R_, radius; _s_, scaphoid; _td_, trapezoid or magnum; _U_, ulna; _u_, unciform; _II-V_, digits. (From Flower's _Osteology_.)

The blow-hole of Whales is, of course, the aperture of the nostrils, which are not so far back in the foetus as in the adult. By the characters of the nostrils the Toothed Whales can be distinguished from the Baleen Whales; in the latter the orifice is double, in the former single. In embryos of Dolphins, however, the two apertures are quite independent. The phenomena of spouting have often been misinterpreted.[231] When the Whale breathes, the expired air rushes out through the nostrils. The water vapour in the breath condenses into drops of water in the cold Arctic regions where the phenomenon has been mainly observed. Hence the idea that water taken in at the mouth is expelled through the blow-hole. As the Whale approaches the surface to breathe, it may be that some of the water of the sea is {346} driven upwards by the forcible expulsion of air from the lungs. But for the most part the water which is spouted is simply condensed breath.

Like some, but not all, other aquatic Mammalia the Whales have apparently no external ear. Indeed the opening of the ear is excessively small. In a huge Rorqual it will "admit a quill"; and although "a quill" is rather vague, we may fairly allow any sized quill without proving that the orifice of the auditory pa.s.sage is anything but exceedingly minute. As a proof, added to so many, that the Whales are the progeny of terrestrial creatures, we have the occasional traces of external ears.[232]

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FIG. 182.--Left lower jaw of foetus of _Balaenoptera rostrata_. Inner aspect, natural size, showing teeth. (After Julin.)

Whalebone Whales never possess permanent teeth as well as the baleen; but in the foetus are more than traces of true teeth, which, however, never arrive at maturity. The whalebone itself is described later (p. 354). That the Whalebone Whales possess teeth while in the foetal condition was discovered so long ago as 1807. It has since been confirmed by many observers. Not only is there one set of teeth developed in the foetal _Balaenoptera_ but two, of which one comes to a greater maturity; the other, in fact, remaining at a very early stage of development. The more complete dent.i.tion belongs to the milk series, as is the case with the Toothed Whales. A very interesting conclusion with regard to the derivation of the simple conical teeth of Whales seems to follow from the development of these structures in Balaenoptera. There are in the young foetus fewer teeth than in the more advanced embryo. Now in the younger embryo some of the teeth are furnished with more than one cusp; they are bi- or even tri-conodont. As Sir R. Owen observed, the teeth--some of {347} them--are literally double teeth. This is a suggestion of the more complicated teeth of the Zeuglodonts, and shows so far that the simple conical teeth of existing Whales (cf. however the Platanistidae) are not by any manner of means so primitive as their actual structure would undoubtedly lead one to believe. Further than this, the greater number of teeth in the older embryo coincided with the disappearance of these double teeth, which seem to split up into the simple conical teeth.

The Toothed Whales are not furnished with baleen, but with teeth only.

These teeth are more or less numerous, their arrangement being of value in the cla.s.sification of the group; a matter which is dealt with later.

In the Narwhal, whose dent.i.tion in the adult is reduced to the well-known tusk or tusks (properly developed only in the male), there is a complete foetal dent.i.tion. A very curious fact has been elucidated by Professor Kukenthal about the dent.i.tion of the Common Porpoise. It appears that in this Cetacean the two teeth corresponding to each other of the two dent.i.tions may fuse into a single tooth, which has in consequence a double crown. It may be that this is the case with the Platanistid _Inia_, and that its diconodont teeth are not, therefore, a reminiscence of the comparatively complicated teeth of the ancient Zeuglodonts.

The internal organs of Whales which show the greatest peculiarities as compared with other mammals are the stomach, the lungs, and the diaphragm.

Whales always possess a complicated stomach divided into many, but into a variable number of, chambers: there are as few as four in some, as many as fourteen in Ziphioids.

On account of its complication the stomach[233] has been compared to that of Ruminants--it has even been alleged that Whales "ruminate"--but the comparison will not hold good. Nor, on the other hand, is there a very close resemblance to the equally-complicated stomach of the Sirenians.

The Rorqual has a stomach with as few compartments as any. The only Whale which appears to have fewer is _Balaena mysticetus_, where there are but three. In the Rorqual the oesophagus opens into a more or less globular sac; from the upper end of this, _i.e._ close to the entry of the oesophagus, arises the second chamber, long and narrowish; then follows an extremely short third sac, {348} then a larger fourth, after which comes the dilated commencement of the small intestine. The latter might be regarded as a chamber of the stomach were it not for the fact that the ducts of the liver and the pancreas open into it. This represents one type of the Cetacean stomach, which seems to be found in all Whales except the Ziphioids. In the latter, the oesophagus opens into the first compartment as usual; but the second division of the stomach arises not close to the entrance of the oesophagus, but at the opposite end. It would seem, therefore, as if the first division of the stomach, found in most Whales, were missing in Ziphioids. This way of looking at the matter is confirmed by the fact that in _Hyperoodon_ a remnant of the missing first stomach is found in the shape of a small diverticulum of the oesophagus just before it enters the stomach.

The essential difference between the Whale's and the Ruminant's stomach is this: in the latter the stomach is primarily divided into two portions, of which the first is non-digestive and is clothed with oesophageal epithelium. The second, the abomasum, is the digestive region. The first part is again divided into three compartments. In the Whales, on the other hand, it is the digestive part which is again subdivided, while if the first part is divided it is not markedly so as in the Ruminants.

The lungs are remarkable for their unlobulated character; in this they agree with the lungs of the Sirenia. The thoracic cavity in which they lie is barrel-shaped, and not, as is usual in terrestrial mammals, boat-shaped, _i.e._ narrower sternally than above. The alteration of the shape of the thoracic cavity is a.s.sociated with the aquatic life; so at any rate the fact that it is also marked in Seals and even in the Otter seems to show.

The Whales are also characterised by the great obliquity of the diaphragm, which is extremely muscular. In this character again we find an agreement with the Sirenia, and also with other aquatic mammals; it is not therefore a character of Whales so much as evidence of an adaptation to the aquatic life. The advantage is, it appears, in the increased capacity of the thoracic cavity, and the consequent greater possibilities of expansion of the lungs, which it must be remembered serve as hydrostatic as well as breathing organs.

Some of the internal arteries of Whales break up into retia mirabilia.

Their kidneys are lobulated; whether this has {349} anything to do with the aquatic life is not so clear. It also characterises the Sirenia, more or less, and the Otters; but, on the other hand, the terrestrial Bears show the same structure as do also some Ungulates. It must be borne in mind, too, that the kidneys of foetal Man are lobulated.

The liver is a compact organ not showing such lobulation as is common, but not universal, among mammals.

The bones of Whales have a somewhat loose structure, and are much impregnated with oil. In many features the skeleton of Whales is highly distinctive of the order.

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FIG. 183.--Skeleton of Porpoise (_Phocoena communis_), _acr_, Acromion process of scapula; _cerv_, united cervical vertebrae; _chev_, chevron bones; _cor_, coracoid process; _hu_, humerus; _hy_, hyoid; _jug_, jugal; _lumb.trans_, lumbar transverse processes; _max_, maxilla; _nas_, nasal; _orb_, orbit; _par_, parietal; _pelv_, vestige of pelvis; _per.ot_, periotic; _pr.max_, premaxilla; _rad_, radius; _rb_^1, first rib; _rb^{12}_, twelfth rib; _sc_, scapula; _s.occ_, supra-occipital; _st_, sternum; _uln_, ulna; _zyg_, prezygapophysis. (From Parker and Haswell's _Zoology_.)

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FIG. 184.--Under surface of the cranium of a young Caa'ing Whale (_Globicephalus melas_). 1/5. _AS_, Alisphenoid; _BO_, basioccipital; _cf_, condylar foramen; _ExO_, exoccipital; _Fr_, supra-orbital process of frontal; _gf_, glenoid fossa of squamosal; _Ma_, body of malar; _Mx_, maxilla; _OS_, orbitosphenoid; _Per_, posterior (mastoid) process of periotic; _Pl_, palatine; _PMx_, premaxilla; _Pt_, pterygoid; _Sq_, squamosal; _tg_, deep groove on squamosal for meatus auditorius externus, leading to tympanic cavity; _Ty_, tympanic; _Vo_, vomer; _ZM_, zygomatic process of malar. (From Flower's _Osteology_.)

The brain case is small proportionately and rounded. The "face" is therefore long, and in some cases, especially among the fossil forms of Platanistidae, the rostrum is extraordinarily elongated. The asymmetry of the Whale's skull is one of its most remarkable features; this, however, is entirely limited to the Toothed Whales, and among them is more p.r.o.nounced in some forms than in others. Thus the Platanistidae and many Ziphioids are not nearly so asymmetrical as the {350} Dolphins and, especially, _Physeter_. This asymmetry affects particularly the premaxillae, the maxillae, and the nasals. The base of the skull is symmetrical. The Whale's skull has very long premaxillae which, however, do not, except in the extinct Zeuglodonts, bear any teeth. The nasal bones, whether symmetrical or the reverse, are very small in existing Whales, which arrangement, together with the long and broad maxillary bones, removes the anterior nostrils, the blow-hole, far backwards. The roof of the skull is not at all formed by the parietals externally. These bones form a portion of the side of the cranium, but are replaced or covered by the {351} enormously-developed supra-occipital in the adult. Here again the Zeuglodonts are more typically Mammalian, for in them the parietals have a normal development and situation, rising even into a median crest as in so many quadrupeds. The bones related to the organ of hearing, the tympanis and petrous bones, are very solid and dense in structure. Moreover they are but loosely attached to surrounding bones, and are thus easily and frequently lost. Nearly the only mammals which resemble the Whales in the fact that the pterygoids sometimes meet in the middle line below are the Edentata (Anteater and Armadillo, see p. 167). But in both groups this peculiarity is not universal.

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FIG. 185.--A section of a skull of a young Caa'ing Whale (_Globicephalus melas_). 1/5. _a_, Angle; _an_, anterior nares; _AS_, alisphenoid; _bh_, basihyal; _BO_, basioccipital; _BS_, basispnenoid; _cd_, condyle; _cp_, coronoid process; _ExO_, exoccipital; _Fr_, frontal; _id_, inferior dental ca.n.a.l; _IP_, interparietal; _ME_, ossified portion of the mesethmoid; _Mx_, maxilla; _Na_, nasal; _Pa_, parietal; _Per_, periotic; _Pl_, palatine; _PMx_, premaxilla; _pn_, posterior nares; _PS_, presphenoid; _Pt_, pterygoid; _s_, symphysis of mandible; _sh_, stylohyal; _SO_, supra-occipital; _Sq_, squamosal; _th_, thyrohyal; _Vo_, vomer. (From Flower's _Osteology_.)

The vertebral column is remarkable for the fact that more or fewer of the cervical vertebrae may be fused together into a short and compact ma.s.s.

This is seen at its maximum in the genera _Balaena_ and _Neobalaena_. The odontoid process of the second {352} vertebra, though hardly at all marked, is nevertheless really present and developed from a bony centre of its own, as in other mammals. The dorsal and lumbar vertebrae are, of course, to be distinguished by the presence of ribs attached to the former; but as there is only a rudimentary pelvis, not attached to the vertebral column, no sacral region can be detected. The caudal vertebrae are to be recognised by the [234]-shaped chevron bones below.

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FIG. 186.--Section through middle line of united cervical vertebrae of Greenland Right Whale (_Balaena mysticetus_). 1/9. _a_, Articular surface for occipital condyle; _e_, epiphysis on posterior end of body of seventh cervical vertebra; _sn_, foramen in arch of atlas for first spinal nerve; 1, arch of atlas; 2, 3, 4, 5, 6, conjoined arches of the axis and four following vertebrae; 7, arch of seventh vertebra. (From Flower's _Osteology_.)

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FIG. 187.--A, Sternum of Greenland Right Whale (_Balaena mysticetus_).

1/15. B, Sternum of Common Rorqual or Fin Whale (_Balaenoptera musculus_).

1/10. (From Flower's _Osteology_.)

The sternum in the Whale tribe is much more modified in the Whalebone Whales than in the Odontocetes. In the latter it is made up of several pieces, as in other mammals, which often, however, become coalesced. In the Mystacoceti this bone is a single piece, to which only one pair of ribs is attached, and its {353} form is characteristic of the genus. It is heart-shaped, more or less, in _Balaena_, and somewhat cross- or [235]-shaped in the genus _Balaenoptera_. In the Odontocetes the ribs have, some of them, the normal attachment by capitulum and tuberculum. In the Mystacocetes the attachment, where it exists, is very loose, and the tuberculum alone is attached to its vertebra. This allows of the freer play of the ribs during respiration. The scapula has a very characteristic form in these animals. The acromion, where it exists, is placed near the anterior margin of the shoulder blade, and overlaps the generally long coracoid process. Clavicles are totally absent. The pelvis is very rudimentary, consisting merely of a single bonelet, to which are attached the rudiments (in some cases) of a femur, and, in _Balaena_ (Fig. 188), of a tibia also.

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FIG. 188.--Side view of bones of posterior extremity of Greenland Right Whale (_Balaena mysticetus_). 1/8. _i_, Ischium; _f_, femur; _t_, accessory ossicle representing the tibia. (After Eschricht and Reinhardt) (from Flower's _Osteology_.)

Whales are to be divided into three great groups:--(1) the Whalebone Whales or Mystacoceti; (2) the Toothed Whales or Odontoceti; and (3) the entirely-extinct Archaeoceti or Zeuglodonts.

SUB-ORDER 1. MYSTACOCETI.

This division is thus characterised:--Teeth are never functionally developed; they are present in the young, but replaced in the adult by the baleen or whalebone; the external respiratory aperture is double; the skull is perfectly symmetrical; the rami of the mandible are arched outwards and do not form a true symphysis; the sternum is always composed of a single piece of bone; the ribs articulate only with the transverse processes of the vertebrae.

The Mystacoceti are nearly invariably huge creatures, the sole exceptions being the Pygmy Right Whale, _Neobalaena_, and {354} a small Rorqual. But even these are larger than the majority of Toothed Whales.

The most characteristic feature by which the Whalebone Whales are to be distinguished from other Whales is that which gives to them their name, the presence of whalebone. Whalebone is a h.o.r.n.y product of the epithelium lining the mouth, and is comparable to an exaggeration of the transverse ridges which are found in the mouths of all mammals upon the palate. In non-Cetacean mammals these ridges vary in depth, and are arranged as a rule transversely, but with an oblique inclination. This is precisely how the plates of baleen are disposed in the mouth of a Whale. Each piece of "bone"

is triangular in shape, the broader end being that of attachment while it narrows gradually; the inner side of the blades is frayed out into a number of threads which form the straining apparatus. The plates vary in length up to as great an extreme length as 13 feet, which occurs in the Right Whale at times. The colour is black or paler, even white. The number of these plates in the mouth is very great. As many as 370 blades have been counted.

They diminish in length towards both ends of the series. Though whalebone has been in use for a long period, whence the whalebone came was formerly one of those things not generally known.

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FIG. 189.--Section of upper jaw, with baleen plates, of _Balaenoptera_.

_a_, Bone of jaw; _b_, gum; _c_, straight edge of baleen plate; _d_, _e_, frayed out surface of baleen plates. (After Owen.)

A very prevalent notion was that the whalebone formed the eyelids or perhaps the eyelashes of the creature. Scaliger, commenting upon Aristotle, held that the whale had "lamellae upon the eyebrows, which, when the head is plunged below the surface, were raised by the water; but when the animal raised its head {355} above the waves the lamellae fell and covered the eyes." Whalebone, too, has been often spoken of as "the fin of a whale,"

"the finnes that stand forth of their mouths." The value of whalebone is still great, in spite of various subst.i.tutes which are now used in its place. In the year 1897, for example, the value of this article was 2000 per ton. As a single Whale may produce several tons of this material, it is not surprising to find that the results of a whaling voyage may be very profitable.