Fig. 3. Specimen 80 e in the Anatomical Museum of the University of Edinburgh. a. The neck of the upper. b. The neck of the lower of the two ribs. The specimen is represented from below, and the drawing much foreshortened.

marked as in the former specimen. In 80 e, 383 b, and in the specimens figured by Knox (Figures 2, 3, 5), the head, neck and tubercle of the higher of the two ribs closely resembled in form the 1st thoracic rib, whilst the corresponding parts in the lower more nearly approached the form of the 2nd rib, so that at first sight many might be inclined to say that the broad bone formed by their junction was due to the blending of the 1st and 2nd thoracic ribs with each other. Fortunately, however, the preservation of the vertebræ with which the ribs articulated in 80 e, enables me to state that this is not the case, and to show that the broad bone is formed by the junction of a cervical with the 1st thoracic rib. The upper head did not, as with the normal 1st thoracic rib, articulate with the upper part of the side of the body of the corresponding vertebra, but with a slightly elevated tubercle at and just above the middle of the side of the body of its vertebra. In this respect it agreed with the arrangement seen in the five specimens of non-ankylosed cervical ribs contained in the University Anatomical Museum. The upper surface of the body of this vertebra had the form of a cervical, the superior articular processes were transversely oval and directed upwards and backwards, and the transverse process, though simulating

in general form that of a dorsal vertebra, and articulating in front with the tubercle of the rib, was directed outwards and a little downwards, and not outwards backwards and upwards, as is the case with the transverse processes of the upper dorsal vertebræ. In its direction this transverse process agreed with those of the 7th cervical vertebra in the specimens, in the museum, just referred to, with which non-ankylosed cervical ribs articulated. The lower of the two heads of the double rib had a double articulation, one half with the lower part of the side of the body of the upper vertebra, the other with the upper part of the side of the body of the lower vertebra, an arrangement of the 1st thoracic rib not unfrequently met with when a cervical rib is developed immediately above it1.

All these characters leave no doubt in my mind that the upper rib-element is a cervical rib, and that the broad shaft in this specimen, and also that in 383 a, are formed by the junction of a largely developed cervical with the 1st thoracic rib. And I believe it may now be considered as proved, what had previously been inferred by Knox, Halbertsma and Huntemüller, but which could only be a matter of inference so long as the vertebral attachments of the two heads were not known, that the specimens described by those anatomists, as well as the one figured by Hunauld (Fig. 2), were formed in a precisely similar manner.

It may be stated therefore for man, as I have already said for the corresponding arrangement in the cetacea, that the bifurcated form of the rib is due, not to the subdivision of a single bone into two parts, but to the fusion of two bones into one mass, the vertebral extremity of which continues to exhibit its fundamental duplex character.

But whilst recognising the general morphological resemblance between these ribs in man and in the cetacea, yet certain features of difference are exhibited, at least by the whalebone whales, to which it is necessary that I should refer. In the Balonoidea the vertebral extremities of the thoracic ribs possess no proper 'head,' and as a rule no 'neck,' and are articulated

1 e.g. Cases 1 and 2 in my paper on non-ankylosed cervical ribs, Vol. IV. p. 130. Through a typographical error on p. 133, the rib attached to the left side of the 12th dorsal vertebra is stated to be 8 inches long and 4 wide, instead of 0.8 inch long and 0-4 wide.

to the vertebræ merely by the tuberosity; their ribs, in consequence, correspond only to those parts of the human ribs which we call the tuberosity and the shaft. In man, when a cervical rib is developed, it invariably-whether fusion with the first thoracic rib does or does not take place-consists of head, neck and tubercle, though its shaft may vary much in length; and the rib takes the place of the anterior transverse process of the vertebra. In the Balanoidea the cervical rib follows the general plan of development of the ribs in these animals, and possesses neither head nor neck, nor does it take the place of the anterior (inferior) transverse process of the vertebra, and it is articulated, like the proper thoracic ribs, with the transverse process of its corresponding vertebra.

When, in man, a cervical rib is blended with the first thoracic, the single bone formed by their junction is by no means uniform in shape, in size, in the place of junction of the two ribs, or in the mode of connection of its sternal end. In Hunauld's case, in Knox's (Figs. 2 and 3), in Sandifort's, and in Huntemüller's the bone possessed only a single sternal articulation; but in Knox's second case (Fig. 5), and in both the specimens, which I have described in this Essay, the bone bifurcated anteriorly, and each branch possessed its own costal cartilage.

Similarly, in the cetacea, differences of a like kind have been seen, which have not necessarily any specific value, and, although the rib in the specimen from the Cape which I have figured, differs in form from the one figured by Dr Gray as Hunterius Temminckii, yet I think it very probable that they are both from the Southern Right Whale.

The consideration of the numerous facts which I have cited and analysed in this paper, has led me to the following conclusions; 1st, that the presence of a cervical rib in man and in the cetacea, whether blended or not with the first thoracic rib, is a mere individual variation; and that just as we should as little think of classifying those men who possess cervical ribs as a genus distinct from the men who do not possess them, so should we as little think to found a genus of whales on the presence of these structures. 2nd. That the genera Sibbaldius, Rudolphius, and Hunterius, so far at least as they are founded on the double-headed character of the ribs, are based on an

inexact conception of the nature of the anatomical peculiarity, and ought no longer to have a place in our systems of classification. My observations therefore support and give strength to the arguments which Van Beneden has advanced in opposition to the view entertained by Dr Gray.

ON THE TRANSVERSE PROCESSES OF THE SEVENTH CERVICAL VERTEBRA IN BALENOPTERA SIBBALDII. BY PROFESSOR TURNER.

THE subject of cervical ribs is so intimately associated with that of the form and the development of the transverse processes of the seventh cervical vertebra, that a brief account of some observations which I have recently made on the latter bone, may not inappropriately follow the preceding paper.

In the cetacea the inferior transverse process on each side of the seventh cervical vertebra is wanting; whilst in B. Sibbaldii, as in other Fin Whales, the vertebræ in front of the seventh (the atlas being excepted) possess on each side a welldeveloped superior and an inferior transverse process, which as a rule uniting externally, form with the side of the body the boundaries of a large ring.

In the course of my dissection of the foetal Balaenoptera Sibbaldii, obtained from the Longniddry Whale, I had the opportunity of examining the vertebral column in an early stage of its ossification, when the vertebræ were, to a large extent, still in the cartilaginous condition. I found that at this early period the seventh vertebra did not differ in the arrangement of its cartilaginous transverse processes from the vertebræ immediately in front: but that with it, as with them, two cartilaginous bars sprang from each side of the cartilaginous body, and curving outwards became continuous with each other at their outer ends, and formed the boundaries of a large ring.

VOL. V.

24

362 PROF. TURNER.

VERTEBRA IN BALÆNOPTERA SIBBALDII.

Hence the differences found, in an adolescent, or adult, Balaenoptera, between the transverse processes of the seventh vertebra, and those immediately preceding it, are not due to differences in their original construction, but to a want of ossification of the inferior, transverse, cartilaginous process of the seventh vertebra, so that it either atrophies, or disappears in the process of maceration. Similarly, the absence of a complete ring, which one sometimes sees in connection with the arrangement of the superior and inferior transverse processes of the sixth or preceding cervical vertebræ in the cetacea, is due to an imperfect ossification of their cartilaginous matrix substance. The species and even genera which have been founded on vertebra which exhibit imperfections in the formation of these rings, are based therefore on specimens in which the process of ossification has not been completed.

My observations on the presence of complete cartilaginous rings in connection with the transverse processes of the seventh vertebra are of especial interest also in reference to a remark recently made by Van Beneden,1 "that in the dolphins of the tertiary period an inferior transverse process is well developed." Hence it would appear that although the dolphins of the tertiary period differ, as regards the development of the inferior transverse process of the seventh vertebra, from adult cetacea of the present fauna, yet that they correspond with the fœtal stage of some of the now-existing cetacea.

1 Bulletins de l'Acad. Roy. des Sciences de Belgique, 1870, No. 12, 376.