The Cambridge Natural History Part 30

_Steno_ comes near _Sotalia_, and Dr. Blanford has transferred to it (under the one name of _Steno perniger_) the two species, _Sotalia gadamu_ and _Sotalia lentiginosa_. It is, however, to be distinguished from _Sotalia_ by the following characters:--Teeth large and few, twenty to twenty-seven on each side of each jaw, with furrowed surfaces to crowns. Vertebrae C 7, D 12 or 13, L 15, Ca 30 to 32. Pterygoids in contact. There are but two species apparently (not counting Dr. Blanford's).

_Tursiops_ is not a very easily definable genus. These are its chief features:--Teeth large, twenty-two to twenty-six in number in each half of each jaw. Vertebral formula C 7, D 12 or 13, L 16 or 17, Ca 27. Pterygoids in contact. Beak distinct. Some five species are allowed; but it seems to be difficult to differentiate the others from _Tursiops tursio_. This, the best-known form, is quite or nearly world-wide in range, and occurs, though not abundantly, on our own coasts. Mr. True has observed that the eyelids of this Whale, which is largely hunted on the American coast, are as mobile as those of a terrestrial mammal. The name "tursio" is derived from Pliny.

Belon would also derive from this word the French vernacular "marsouin."

The latter term is sometimes regarded as a corruption of "Meerschwein," but it would seem to be more probably derivable from "marinum suem," from the Latin direct. _T. tursio_ has the back black to lead-colour; the under parts white. In the reputed species, _T. abusalam_, from the Red Sea, the back is a dark sea-green. _T. tursio_ reaches a length of 12 feet, but is more usually smaller.

The genus _Tursio_ must be carefully distinguished from {380} _Tursiops_.

It has no dorsal fin, the teeth are small and numerous (forty-four), and the pterygoids are separate. There are two species, _T. borealis_ and _T.

peronii_, the former being northern and the latter more widely spread.

The genus _Cephalorhynchus_ has for its chief characters the following:--Teeth twenty-five to thirty-one, small and sharp. Pterygoids widely separated. Dorsal fin not falcate, but triangular or ovate in form.

Beak not well marked off from the head. The species of this genus are all southern in range; four are perhaps to be allowed.

FAM. 3. PLATANISTIDAE.--This family of Odontocetes may be distinguished from the Dolphins by the following a.s.semblage of structural features:--Cervical vertebrae all free, and each one of some length (for a Cetacean). Jaws long and narrow, with a considerable length of symphysis.

Teeth very numerous.

This very meagre series of differential characters is largely due to _Pontoporia_ on the Platanistid side, and to _Monodon_ and _Delphinapterus_ upon the Delphinid side. Otherwise the family Platanistidae would be extremely distinct. The two last-named genera have separate cervical vertebrae, and in the Beluga at any rate this is expressed externally by a quite distinct neck. Moreover, as Mr. True has pointed out, the pterygoid bones have not the involuted cavity below which characterises other Dolphins; and they have, what other Dolphins have not, an articulation outwards with the roofing bones of the skull. Sir W. Flower described the fact that in Inia (and the same occurs in Pontoporia) the palatines are separated from each other by the intervention of the vomer. In this feature they resemble certain Ziphioids, _Berardius_, _Oulodon_ (= _Mesoplodon_) _grayi_, and _Hyperoodon_. The true Dolphins also appear to show the same intervention of the vomer in a few cases. There is nothing, therefore, distinctive from the Delphinidae in this feature.

The existence of cartilaginous sternal ribs in _Inia_ and _Platanista_ shows affinity between these two genera and the Physeteridae. _Pontoporia_ is Dolphin-like in this particular, as it is also in the mode of articulation of the ribs with the vertebral column. But this last matter has already been dealt with. The princ.i.p.al reason for placing _Pontoporia_ with the other two genera is the close resemblance which its skull bears to that of _Inia_.

The first genus of this family which will be noticed is _Platanista_. {381} The following are its main characters:--Dorsal fin absent. Eyes rudimentary. Pectoral fins large and truncated at the extremity. Teeth, about twenty-nine in each half of each jaw. Scapula with the acromion coinciding with its anterior edge. Skull with enormous maxillary crests, and with the palatines entirely concealed by the pterygoids. The length of the above definition will serve to indicate how anomalous in many particulars is the structure of this "Dolphin."

There is apparently but one species, _P. gangetica_, the "Susu." The Indian vernacular name is derived from the sound that the animal makes when spouting. It is an inhabitant of the Ganges and the Indus, together with their tributaries, and ascends very high up its streams. It is also thought to be purely fluviatile and never to desert the rivers for the sea.

_Platanista_ lives chiefly by grubbing in the mud for prawns and fish.

Grains of rice have also been found in the stomach, but this would seem to be accidental. The long snout of the Susu has been compared to the long snout of the Gharial, a native of the same region. This Whale grows to a length of over 9 feet, but this length is exceptional. Its anatomy has been elaborately described by Dr. Anderson.[262]

The next genus, _Inia_, is thus to be characterised:--Dorsal fin rudimentary; pectorals large and ovate. Teeth, as many as thirty-two on each side, often with an additional tubercle. Skull without large maxillary crests; palatines not hidden by pterygoids, but divided by vomer. The vertebrae of this genus are few in number, only forty-one in all, which are thus distributed: C 7, D 13, L 3, Ca 18. The peculiarities of the vertebral column are several. In the first place, as has been mentioned in the definition of the family, all the cervicals are separate and individually of some length. Secondly, the axis has a better trace of an odontoid process than in any other Whale except _Platanista_, where it is even more obvious. The lumbar region is remarkable on account of its restriction to three vertebrae. The sternum, by what we must regard as convergence, is somewhat like that of the Whalebone whales. It consists of one piece only, of a roughly-oval form, to which apparently only two pairs of (cartilaginous) sternal ribs are attached. In the fore-limb the proportions between the humerus and the radius are more like {382} those of terrestrial mammals; _i.e._ the humerus is distinctly the longer, the converse usually obtaining among Whales. But _Platanista_ again agrees with _Inia_. The teeth are remarkable for the fact that the hindermost ones of the series have an additional lobe; they are not purely conical as are those of Whales generally.

There is but one species, _Inia geoffrensis_, which inhabits the Amazons, and grows to a length of 8 feet. Its colour variations are rather extraordinary, unless they can be set down to s.e.x, which has been denied.

Some individuals are wholly pink; others are black above and pink beneath.

This Whale is believed by the Indians to attack a man in the water, and it is added that the _Sotalia_ of the same streams will defend him from these attacks! Naturally, therefore, superst.i.tious reverence attaches to this Dolphin, which is tiresome to the naturalist who wants specimens, as Professor Louis Aga.s.siz found.

In the genus _Pontoporia_[263] the dorsal fin is well developed and falcate. The teeth are very numerous, 200 in all. The ribs articulate as in Dolphins. The skull closely resembles that of Inia, and the scapula is, as in that genus, "normal."

The proper name for _Pontoporia_ is really _Stenodelphis_, which name was first used by Gervais a month or two before Gray, who separated it from the vague _Delphinus_ of its original discoverer, Gervais himself. It has a longer snout than _Inia_, which, being bent towards the extremity in a downward direction, curiously suggests the skull of a Curlew. In details, however, the skull is exceedingly like that of _Inia_. It is nearly symmetrical. The vertebral formula appears to be the following:--C 7, D 10, L 5, Ca 20 = 42, just one over the number of the vertebrae in _Inia_. The sternum is in two pieces. Of the ten pairs of ribs the first three are double-headed. These and the next have sternal moieties joining the sternum, of which the first three are ossified, the last being apparently merely a ligament.

There is a single species of the genus, _P. blainvillii_. This Whale is described by Mr. Lydekker as being of a clear brown colour, harmonising with the waters of the estuary of the Amazons and the La Plata which it inhabits. The same colour characterises _Sotalia pallida_ of those parts of the world, and {383} may be a colour adaptation. But the extant accounts of the colour of this Dolphin vary--quite possibly in accordance with real variations, such as are exhibited by _Inia_ already spoken of. _Pontoporia blainvillii_ is a smallish Dolphin some 4 feet in length.

FOSSIL ODONTOCETES.--Several of the existing genera of Dolphins are also known in a fossil condition, as well as Ziphioid Whales closely related to existing forms. We shall deal here only with a few genera of fossil Odontocetes which depart in their structure from existing forms.

The genus _Physodon_ is Miocene, and has been found in Patagonia. It appears to be most nearly allied to the Physeteridae, but should probably form a distinct family. _Physodon_ was not so large as _Physeter_, the skull measuring only some 10 feet. It thus comes nearer in point of size to _Kogia_, and it is interesting to note that its relatively-shorter snout is also suggestive of the dwarf Cachalot. The general outline of the skull is, however, more like that of _Physeter_, and there is the same deep cavity for the lodgment of spermaceti. The main feature of interest in the skull is the presence of teeth in both jaws, and the fact that two or three are lodged in the premaxillae. This is precisely what is found in the most ancient Whales, the Zeuglodonts.

Extinct Dolphins, apparently referable to the Platanistidae, are the most numerous among the earlier forms of Cetaceans, and it is significant that the earliest known forms of these go back to the Eocene.

The genus _Iniopsis_ of Mr. Lydekker,[264] with one species, _I.

caucasica_, comes from rocks which seem to be of that age. The back part of the skull of this animal, the only part of the skull known, has the same squarish excavation of the maxillaries that characterises _Inia_ and _Pontoporia_. Its lower jaw was slender and possessed numerous teeth.

The long snout and jaws of Platanistids, especially exaggerated in _Pontoporia_ among living forms, are constantly found in these Tertiary Platanistids.

_Eurhinodelphis_ had a beak three and a half times the length of the cranium, whereas in _Pontoporia_ the proportions are as 2:1. The teeth too were very numerous.

The genus _Argyrocetus_, from Patagonian Tertiary strata, was an animal about as large as the existing Dolphin. It had the {384} slender rostrum and numerous teeth of the Platanistids and the squared excavations of the maxillaries. _Argyrocetus patagonicus_ possessed also archaic characters, suggesting earlier affinities still. The two condyles of the skull instead of being closely adpressed to the skull stood out in a way more like that met with in terrestrial mammals. The nasal bones instead of being abbreviated rudiments are well developed as in the archaic Zeuglodonts. The cervical vertebrae of this Whale are all perfectly free from each other and individually long. The skull is on the whole bilaterally symmetrical; this again is a feature more p.r.o.nounced among the Platanistidae than among other Odontocetes. Accompanying these generalised Cetacean characters are some which show that the animal was too specialised to be the direct ancestor of any existing forms. The end of the mandible was upturned and without teeth, its form being quite unique among Cetacea. Other allied forms, such as _Zarrhachis_ and _Priscodelphinus_, showed the same length of the cervical vertebrae.

A very distinct family of extinct Whales is that of the SQUALODONTIDAE.

They to some extent bridge over the gap between the existing Odontoceti and the Eocene Archaeoceti (Zeuglodonts).

The skull of these Whales was on the whole Dolphin-like. But they possessed teeth which were distinctly specialised into incisors, canines, and molars.

The molars have a coa.r.s.ely-serrated cutting edge as in the Zeuglodonts, and are also to some extent two-rooted. But they are more numerous, and so far approximate to the conditions which characterise the more typical modern Odontocetes. _Squalodon_ was a long-beaked form, and _Prosqualodon_ had a skull whose proportions are nearer those of _Kogia_.

SUB-ORDER 3. ARCHAEOCETI.

This division of the Whale tribe embraces but a single family, ZEUGLODONTIDAE, of which but a single genus, _Zeuglodon_, can with certainty be discriminated.

_Zeuglodon_ is an Eocene form of large size, with teeth which are limited in number and disposed in three series as incisors, canines, and molars.

The molars are double-rooted, a fact which has given to the genus its name.

The nasal bones being long {385} instead of rudimentary like those of other Whales, the blow-hole lies more in the middle of the face. The skull, too, is not Whale-like in a number of other points. Thus the premaxillaries take their fair share in the outline of the upper jaw; and, furthermore, bear the incisor teeth. The parietals meet above in a crest and are not excluded from the roof of the skull. The vertebrae of the neck are in no way shortened; neither are they fused together. The ribs are double-headed, and the sternum is made up of several pieces. Some naturalists, particularly Professor D'Arcy Thompson,[265] have a.s.signed a relations.h.i.+p to the Seals to these ancient Cetacea; but others[266] have disputed this view chiefly on the grounds that the characters which appear to be Seal-like are simply characters which are generalised and so far at most not Whale-like. Thus the long neck and the serrated character of the teeth may be accepted as Seal-like on the one hand; but on the other, a simple serrated tooth and a long neck are not by any means features of organisation which we should consider out of the way in an ancient form of Cetacean which probably preyed upon fish. The humerus of _Zeuglodon_, according to Mr. Lydekker, puts out of court any possible near relations.h.i.+p to the Seals. But the matter under dispute can be further studied by reference to the three memoirs quoted below.

{386}

CHAPTER XIII

CARNIVORA[267]--FISSIPEDIA

ORDER VII. CARNIVORA

This order may be thus defined:--Small to large quadrupeds, terrestrial, arboreal, or aquatic, of usually carnivorous habits. The teeth have generally sharp and cutting edges, and the canines are well developed; the incisors are small, and four to six in number. The number of toes is never less than four. There are usually strong and sharp claws. The clavicles are incomplete or absent. In the hand the scaphoid and lunar bones are always united. The brain is well developed, and the hemispheres are well convoluted. The stomach is always simple, while the caec.u.m, if present, is always small. The members of this group have a deciduate and zonary placenta.

The fewness of the characters used in the above definition is chiefly owing to the fact that the Seals and Sea-lions, although they are referable without a doubt to this order, have undergone in their metamorphosis into aquatic animals so many changes that some of the main features in the structure of their terrestrial relatives have been lost. This group will, however, be again characterised. We shall deal at present with the land division of the Carnivora, the CARNIVORA FISSIPEDIA as they are generally termed. The name is of course given to them to distinguish them from the corresponding division of the PINNIPEDIA. In the latter group the feet and hands are modified into "fins"; in the other the fingers and toes are cleft, as with terrestrial beasts generally. {387}

SUB-ORDER 1. FISSIPEDIA.

[Ill.u.s.tration]

FIG. 190.--Under surface of the cranium of a Dog. . _apf_, Anterior palatine foramen; _AS_, alisphenoid; _as_, posterior opening of alisphenoid ca.n.a.l; _BO_, basioccipital; _BS_, basisphenoid; _cf_, condylar foramen; _eam_, external auditory meatus; _ExO_, exoccipital; _flm_, _flp_, foramen lacerum medium and posterius; _fm_, foramen magnum; _fo_, foramen ovale; _Fr_, frontal; _fr_, foramen rotundum; _gf_, glenoid fossa; _gp_, post-glenoid process; _Ma_, malar; _Mx_, maxilla; _oc_, occipital condyle; _op_, optic foramen; _Per_, mastoid portion of periotic; _pgf_, post-glenoid foramen; _Pl_, palatine; _PMx_, premaxilla; _pp_, paroccipital process; _ppf_, posterior palatine foramen; _PS_, presphenoid; _Pt_, pterygoid; _sf_, sphenoidal fissure or foramen lacerum anterius; _sm_, stylomastoid foramen; _SO_, supraoccipital; _Sq_, zygomatic process of squamosal; _Ty_, tympanic bulla; _Vo_, vomer. (From Flower's _Osteology_.)

A very marked feature of the terrestrial Carnivora is to be found in the structure of the teeth. The incisors are nearly always six, and are somewhat feebly developed in many cases. The canines are almost invariably very large strong teeth, and are always present. In some of the extinct Cats they reached enormous dimensions. The number of cheek teeth is not always identical; but the last premolar in the upper jaw and the first true molar in the lower jaw, known as the "carna.s.sial" or "sectorial" teeth, mark a difference in structure between the anterior and the posterior crus.h.i.+ng teeth; those in front of the carna.s.sial tooth have cutting edges, and are often merely small, conical teeth; those behind have broader crowns and are tuberculate; those of simpler forms often trituberculate; those of others {388} with numerous tubercles. The carna.s.sial tooth is often, but by no means always, very much larger and especially longer than the rest of the molar and premolar series. It is less p.r.o.nounced in some of the omnivorous Arctoidea. The skull of the Carnivora is longer in the more primitive types, such as the Canidae, and shorter in the more specialised Felidae. The orbit is hardly ever completely shut off by bone, though the pos...o...b..tal process of the frontal sometimes approaches the corresponding upward process of the zygomatic arch. The palate, which is completely ossified, sometimes reaches back for some distance behind the teeth; it always extends as far as the last molar. The tympanic bulla is often very inflated, and if flatter, as in the Bears, is at any rate large and conspicuous. The lower jaw has a high coronoid process, and the condyle is transversely elongated, this part of the bone being rolled into an almost cylindrical form; it fits very closely into the glenoid cavity, and the articulation is thereby very strict--an obvious advantage in a creature with so great a need for power of jaw.

[Ill.u.s.tration]

FIG. 191.--A, Atlas of Dog. Ventral view, . B, Axis of Dog. Side view, 2/3. _o_, Odontoid process; _pz_, posterior zygapophysis; _s_, spinous process; _sn_, foramen for first spinal nerve; _t_, transverse process; _v_, vertebrarterial ca.n.a.l. (From Flower's _Osteology_.)

In the vertebral column the atlas always has large wing-like processes; the spine of the axis vertebra has a long antero-posteriorly elongated form.

The transverse processes of the fourth to the sixth cervicals are, as a rule, double. These features, however, though characteristic of the Carnivora are not by any means distinctive. The true sacrum consists of but a single vertebra to which the ilia are attached; but at most two other vertebrae are fused with this. The clavicle is always small and sometimes quite rudimentary, or even absent. The spine of the scapula is well developed, and almost equally divides the {389} surface of that bone. The digits of the Carnivora are mostly five, and are never less than four. The mode of progression may be digitigrade or plantigrade, and the intermediate semidigitigrade mode of walking also occurs. The brain in all Carnivora is large and well convoluted. The arrangement of the convolutions is characteristic. There are three or four gyri disposed round each other, of which the lowest surrounds the Sylvian fissure. The stomach in these creatures is always simple in form, without {390} subdivisions. The caec.u.m is never large, and may be, as in the Bear tribe, completely absent.

[Ill.u.s.tration]

FIG. 192.--Brain of Dog. A, Ventral; B, dorsal; C, lateral aspect. _B.ol_, Olfactory lobe; _Cr.ce_, crura cerebri; _Fi.p_, great longitudinal fissure; _HH_, _HH_^1, lateral lobes of cerebellum; _Hyp_, hypophysis; _Med_, spinal cord; _NH_, medulla oblongata; _Po_, pons Varolii; _VH_, cerebral hemispheres; _Wu_, middle lobe (vermis) of cerebellum; _I-XII_, cerebral nerves. (From Wiedersheim's _Comparative Anatomy_.)