The external malleolus of the tibia is divided by a deep groove, for the passage of a tendon, into an anterior and posterior tubercle; from the latter of which, and close to the edge of the articulating surface, arises a strong and broad ligament, that is inserted into the os calcis. Under this lies another ligament, which, arising from the anterior tubercle, is also inserted into the os calcis. It is to be observed, that the origin of the latter is anterior to that of the former, but its insertion posterior, so that these lateral ligaments cross each other in the form of an x. The external articulating protuberance of the astragalus on which the tibia revolves, has, as has been already stated, a nearly circular outline, and the attachments of the ligaments just described, are at points on the outside of the os calcis, which would lie nearly in the circumference of that circle, were it continued from the articulating surface; so that each of these ligaments has one of its extremities fixed in a certain point of the circumference, while its opposite extremity revolves during the motion of the joint, nearly in the circumference of the same circle. This observation applies likewise to the two lateral ligaments on the inner side of the joint, which have nearly the same relation to each other, and to the general contour of the joint, as that just described; so it is obvious, that during the rotation of the joint, as the origins of these ligaments move along the same circumference in which their attachments are fixed, the ligaments will be most stretched when they correspond to diameters of that circle.

Now it is so arranged that this happens at the same time for all, and consequently the ligaments on each side correspond not merely as to direction, but as to the point of time they become most stretched, which is nearly at the moment that the joint has no tendency to move either way, and at that moment, it is to be observed, that although the ligaments are most tense, and of course react on their points of attachment with greatest force, yet this produces no motion, as the force is exerted in a direction perpendicular to the circumference; but as soon as the tibia is moved beyond this point of inaction for the ligaments, the latter, no longer representing diameters, by their contractile force evidently tend to accelerate the motion; and as they all act in the same direction, and are assisted by the shape of the arti

culating surfaces, a sudden motion of flexion or extension is thus produced.

The preceding explanation supposes the ligaments of this joint to possess, contrary to the nature of ligaments in general, a certain degree of elasticity, which was evidently the case in all, but particularly in the most deep-seated of those on the inner side of the joint, which, therefore, appears most concerned in producing the sudden motion, whether of flexion or extension.

In the autumn of 1829, two of the species of whale called Delphinus diodon, by Hunter, Hyperoodon, by La-Cepede, and Cetodiodon, by Dr Jacob, were captured near Dublin, one of which, measuring about sixteen feet in length, I procured for the purpose of preparing its skeleton.

After the spinal column had undergone maceration for a few days, I found that the intervertebral substance could be easily detached from the bodies of the vertebræ, and that it carried with it, firmly attached to each of its extremities, a flat circular bone, about a quarter of an inch in thickness, and exactly corresponding in the extent and shape of its surface, to the surface of the body of the vertebra, from which it had been separated.

The separation was effected with facility, and took place spontaneously and completely when the maceration had been continued some time longer.

The surface of the flat bone, where it had been adherent to the body of the vertebra, was of a spongy texture, afforded a passage to many blood vessels, and was marked by numerous sharp projections and deep furrows, diverging from its centre, and answering to similar projections and furrows on the denuded extremity of the vertebra; of course the surface of these bones varied in shape and size with the extremities of the vertebræ to which they were attached, being from five to six inches in diameter at the dorsal, and not more than one inch at the last caudal vertebra..

The substance of these bones towards the intervertebral substance was of much harder and closer texture than that of the bodies of the vertebræ themselves, and where it was adherent to

the intervertebral substance, it had a smooth surface, marked with a great number of concentric lines, answering to the arrangement of the fibres in the intervertebral tissue, which adhered to this face of the bone with great strength. This marking was deficient towards the centre where the intervertebral substance is fluid.

The facility with which these bones are detached, is the reason why we never find them adhering to the vertebræ of those young whales which have been wrecked on our coast, and whose skeletons have been exposed to the action of the waves and the weather. Their flat shape, too, renders them liable to be covered by the sand, and hence I have never known them to be found separately, even when the vertebræ and other bones of this species of whale were scattered along the coast in great numbers, as happened at Dungarvan some years after several of these animals had been captured and dragged ashore by the fishermen *.

The bones I have described must evidently be considered in the light of terminal epiphyses of the bodies of the vertebræ, and are deserving of notice on account of the facility with which they can be detached, even in very large, and of course not very young, animals of this species, as I observed in the two skeletons preserved in the College of Surgeons, one of which measures thirty feet in length; so that when the skeleton has been artificially prepared, they resemble separate intervertebral bones rather than vertebral epiphyses. In the land mammalia the consolidation takes place much more rapidly, and a few years are sufficient to efface all traces of former separation between the epiphysis and the body of the vertebra; the comparative slowness of this process in the whale, is probably referrible to the longevity of the animal, and the greater length of time necessary to complete its growth. A knowledge of this fact puts us in possession of a new and useful mark of the animal's age, independent of its size, and it is for this purpose I have brought it forward, for although not noticed by any author I have seen

• Many years ago we picked up several of these intervertebral looking bones, upwards of a foot in diameter, on the shore of the island of Yell, one of the Shetlands. In their neighbourhood was a skeleton of a whale, about 40 feet long, part of which we brought to Leith.-EDIT.

on the Anatomy of Whales, it must, nevertheless, have been known to several. If we find that the terminal epiphysis has become completely united to the body of the vertebra, we may be assured that the bone, whether large or small, belonged to an animal arrived at maturity; but if not, we may conclude that it had not yet attained to its greatest size. To facilitate this inquiry, I may remark, that a very slight examination of a vertebra is sufficient to determine, whether the epiphysis has or has not been detached; as in the former case the surface is marked by deep ridges and furrows diverging from the centre towards the circumference; whereas in the latter, if the animal was of moderate size, the marking consists of concentric lines, answering to the attachments of the intervertebral substance; and if the individual was very large, these concentric lines are exaggerated into concentric furrows; and whether the attachments of the intervertebral substance be marked by concentric lines or by concentric furrows, a considerable portion of the central part of the bone, where it had been in contact with the internal substance of the intervertebral ligaments, is quite destitute of this marking, and presents a striking contrast to the rest of the surface.

I am not aware that the true cause of this remarkable difference between the markings on the extremities of the vertebræ of the cetacea has been before explained.

It may not be uninteresting. to add, that the cranium of the Delphinus diodon in my possession, and both those in the Museum of the College of Surgeons, present, in a very remarkable manner, the want of symmetry between the right and the left sides of the cranium, which was first observed by Meckel in the skulls of the cetacea.

Note. Since the preceding notice concerning the hock-joint of the horse, was submitted to the Academy, I have had an opportunity of examining two horses affected with string-halt, and am inclined to attribute the disease to a spasmodic affection of the flexors of the limb generally, rather than to any derangement in the structure of the hock-joint. It may be right to mention, that the following authors on Comparative Anatomy, and the Anatomy of the Horse, have been searched, but they contain no notice of the peculiarity in the structure of the hock-joint, above described :—Macartney, Cuvier, Carus, Blumenbach, Meckel, Clater, Blaine, Stubbs, Percivall, Boardman, White, Lawrence, Osmer, Home, Bourgelat.

On the Lacustrine Basins of Baza and Alhama, in the Province of Granada in Spain. By Colonel SILVERTOP, M. G. S. I. Communicated by the Author.-(Concluded from former volume, p. 349.) With a Plate.

BASIN OF ALHAMA.

THE geographical position of this basin was alluded to in general terms at the commencement of my last communication. It occupies a large circular area, at the distance of about fifty miles to the south-west of that near Baza, on the northern side of the primitive and transition chain of mountains which border the Mediterranean; and it is chiefly surrounded by primary rocks towards the south and east, and by ridges of secondary limestone towards the north and west *. In the latter, close to a town called Loja, at the western extremity of the basin, there is a chasm through which the river Genil †, rising in the Sierra Nevada to the east of Granada, is enabled to escape, and to pursue its course to the Guadalquivir; but beyond this chasm the secondary limestone is continued, and, circling round towards the east north-east, forms the boundary of the basin towards the north. A considerable portion of this ridge is known by the name of Sierra de Cogollos, and the distance from it to the opposite ridge near Alhama, may be taken as the greatest length of the basin; that from a village called Escuzar, on its eastern side, to the town of Loja, as its greatest breadth; the former being equal to about thirty-six, the latter to about thirty miles. One insulated group of transition limestone, named La Sierra de

* In the southern boundary of this basin, a junction between the primary and secondary rocks occurs between a pass called El Puerto de Zafarraya and the western flank of a high mountain, well known to botanists, and called La Sierra de Tejeda: in the northern boundary a similar junction takes place, near a village called Huetor de Santillana, about four miles from Granada, on the road to Guadiz. At neither of these points, however, is there any interruption of continuity in the bounding ridges, the secondary limestone in both instances appearing to come in contact with, and to rest upon, primary rocks of a similar composition or basis; that near Huetor being a granular, that of Tejeda a lamellar limestone, and both highly crystalline.

+ The classic vale, the Vega de Granada, watered by the Genil, has been immortalized in song and in prose, as the theatre of many a chivalrous deed in the olden times.

OCTOBER-DECEMBER 1830.

E