fissures, that leave between them thin plates or laminæ *. These laminæ are formed by fibres that radiate from the axis to the circumference of the different cylinders †. The plates of the cylinders are about the thickness of a shilling; and the spaces interposed between two plates, though not always equal, are generally four or five times larger than that which is occupied by the thickness of the cylindrical plate. The cylinders were nearer to one another towards the centre and the circumferences, than in the space interveping ‡. In four places, two on the dorsal and two on the sternal aspect, the fissures or sulci penetrate through all the cylinders ||. These four deep sulci serve for the attachment of two cartilaginous tubes, that run longitudinally on the vertebral column; the one on the dorsal aspect, containing the spinal marrow, and that on the sternal aspect, the large blood vessels §. What occasions a singular appearance in these vertebræ, is their want of processes. In the vertebræ of many fishes, we observe nothing like articular processes; but in these vertebræ there are neither transverse nor spinous processes, nor any thing calculated to suggest an idea of them. These vertebræ, therefore, are susceptible of inflection to an equal extent dorsad, sternad, dextrad and sinistrad. *Plate x. fig. 3. d. + Id. fig. 4. f. Dd 2 + Id. fig. 5. a, b, c. Another remarkable appearance, and which still may be observed in those vertebræ which are preserved in the Museum of the University, is the difference of diameter, and the difference of length, that occur alternately as you pass in succession from the one to the other; a larger vertebræ being interposed between two that are smaller, and a smaller interposed between two that are larger *. In the first set of vertebræ which I saw, taken from the caudal or sacral extremity, according to what I conceive a most accurate report, (that of Mr Urquhart, a gentleman who saw the animal, and a gentleman, too, of respectability and education, and well-known to our President and Secretary to be ardent in his pursuit of natural history), none of them seemed to taper like a cone, but regularly preserved the cylindrical form, the larger and the smaller vertebræ, as they occurred alternately, gradually becoming less and less than the preceding of the same kind, as they approached the caudal extremity. The cause of this singular structure I cannot explain, unless it be to favour the action of the muscular fibres, which, by this contrivance, must have entered the two contiguous vertebræ at less acute angles than if they had been more parallel to the axis. If this be the reathe difference of diameter in contiguous vertebræ becomes a substitute for the processes that are wanting, and, like the processes, is made to son, * Plate x. fig. 3. furnish more advantageous levers for the muscles. In systematic connection, the contiguous vertebræ present to one another the bases of their cones, united by an intervertebral ligament *. The intervertebral space over which it stretches, is from two to three quarters of an inch. The ligament itself is very elastic, and about a quarter of an inch in thickness. It is composed of different strata, and each stratum of circular fibres. These strata form the inner side of the base, where they firmly adhere; are reflected on the inner side of the two cones, towards their apex † ; but always thinner as they advance from the base to the apex, forming every where the lining or internal stratum of the two cones. In the wet state, the ligament where it is reflected on the inner side of the cones, resembles a ligamento-cartilaginous substance in the dried state. This appears under the form of a strong dense membrane. The cavity formed by the two cones and the ligament was filled with a fluid, opaque, whitish, and fetid; but became less opaque, white and fetid, when exposed to the heat of boiling water. One use of this fluid in the vertebræ of fishes, is well known; it is the ball on which the vertebræ move with the least possible degree of friction, and is infinitely superior to the ball and socket joint in the works of art. There is something similar |