In the Mysticete, or common Whalebone Whale (of which a side view of the skull is given atfig. 249) the immense maxillary bones ( a, a) are compressed, and disposed each like an expanded arch along the outside of the in termaxillaries ( b ) and the vomer; their inferior surface has two facets separated by an interme diate longitudinal ridge, to the sides of which the plates of whalebone or baleen are attached (b, fig. 259). The intermaxillary bones are also laterally compressed, and diverge from each other posteriorly to form the long elliptical bony outlet of the nostrils; this orifice is com pleted behind by the nasal bones, which are of very small size, and are partially covered by the frontal bones, which project forwards above them in the form of two small points. The tranverse portions of the frontal (c) and max illary (as) bones, which contribute to form the orbits, extend obliquely backwards : the tem poral bone (d) is of an irregular quadrate form, and extends much further backwards even than the occipital condyles. The occipital bone ( e) advances forwards so as to cover almost all the upper part of the cranium, where it presents a general convexity. Each ramus of the lower jaw (f) is convex exter nally, compressed and somewhat trenchant both at the upper and lower margins. The coronoid process, on which the letter is placed, is in the form of a slightly raised obtuse angle; the condyloid process (g ) forms the large tube rosity behind. It is articulated to the glenoid cavity by a mass of ligamentous fibres, and not by a capsular ligament surrounding a synovial cavity.
The vertebral column of the Cetacea does not differ from that of other mammalia except in the modifications demanded by their peculiar mode of existence. The cervical vertebrw, of the normal number of seven, with the exception of the Manatee, are in general extremely thin, and though in some species, such as the Manatee, the Dugong (k, fig. 246), and the Platanista, they are found free; others, as the Dolphins and Porpesses, have the first two commonly anchylosed together. In the Bake noptera: the dentata is anchylosed at its upper part to the third cervical vertebra. In the Cachalots they are the six last vertebrw which are thus found united to one another, and in the Whales, properly so called, or Bal.tnee, all the seven are anchylosed. (Seefig. 250.) The dorsal vertebrw (1,fig. 246), the number of which varies accordinc, to the species, are characterized by having their spinous processes, bent backwards, elongated from the first to the last, and equalled in length by the transverse processes. Moreover, their posterior articu lating processes disappear after the first ver tebra, and the anterior ones soon cease to per form the functions of parts concerned in the union of the vertebrw to one another.
In fig. 251, which represents the eleventh dorsal vertebra of the Cape Whalebone Whale, a is the spinous ; b, b, the two transverse, which begin to lengthen from this point in the succeeding vertebrm, c, c, the anterior articu lating processes.
The lumbar vertebrae (m, fig. 246), the posterior limit of which it is difficult to deter mine in animals devoid of pelvis, have their spinous (a, fig. 252) and transverse processes (b) very long. The first are straight and slightly inclined backwards.
As it is essential that the Cetaceans should have the posterior part of their vertebral co lumn left free, to allow of the vigorous in flexions of the tail required in the act of swimming, none of the vertebrae are anchy losed together or encumbered by a union with posterior extremities, and hence there are none which can be properly termed sacral, unless we regard the sacrum as represented by the single vertebra, (n, fig. 246,) to which, in the
Dugong, the pelvic bones are suspended. The caudal vertebrw may then be considered to commence from this point. Most of these vertebrx (o, fig. 246) are further charac terized by the chevron bones, (p, figs. 246, 253,) which at first are strong and well deve loped, but together with the other processes gradually diminish and disappear towards the extremity of the vertebral column, where the centres or bodies of the vertebrae alone appear, and present a depressed flattened form cor responding to the horizontal position of the caudal fin, which characterises these air-breath ing inhabitants of the ocean.
Fig. 253 represents one of the anterior caudal vertebrw of the Cape Whale : a is the spinous ; b the transverse; c, c, the represen tatives of the an terior oblique pro cesses ; p the in ferior spinous pro cesses, or chevron bones.
To bones so lit tle mobile, and so rudimental as the vertebrw of the neck in Cetace ans, muscles pro portionately de veloped should correspond, and such in fact is the case. The cervical muscles in these animals are the same in number as in other Mammals, but their short ness and thinness, principally in those at tached to the atlas and the axis, are extreme; and although those which proceed from the other •cervical vertebrm may be better charac terized, their action, nevertheless, is not much more extensive.
The muscles of the back present no other important modifications than their great deve lopment and their prolongation even upon the coccygeal vertebrx. Thus the longissimus dorsi and the sacro-lumbalis are attached anteriorly to the skull, and posteriorly transmit their ten dons, the first to the end of the tail, the second to all the transverse processes of this part of the spine, associating in this way the move ments of the back with those of the tail. As to the muscles peculiar to the tail, besides those which belong to this organ in all Mammals where it exists as a moveable organ, there are besides, in the Cetaceans, 1st, the antagonists of the sacro-lumbalis below the transverse pro cesses ; 2nd, a levator caude, which takes its rise above the five or six dorsal vertebrw, under the longissimus dorsi, and often in this part blends with it ; it then extends freely as far as the extremity of the tail, where the two muscles unite together again by their tendons ; 3rd, a depressor muck, of great thickness, which pro ceeds from the pectoral region, and spreads its tendinous processes upon the ribs, distributes them laterally to the transverse processes, and below to be inserted into the chevron bones along the two posterior thirds of the tail; 4th, a muscle which comes from the rudimental bones of the pelvis, and is inserted into the chevron bones of the anterior portion of the tail ; 5th, the great recti muscles and the obligui ascen dentes, which, proceeding from the abdomen, attach themselves behind to the sides of the base of the tail.