OCR Text |
Show 486 DR. H. BURMEISTER ON PONTOPORIA BLAINVILLII. [May 9, longer a true transverse process, but only a sharp lateral crest perforated at the base by a perpendicular foramen. This perforation is also seen on the sixth, seventh, and eighth vertebrae, but becomes somewhat more directed to the centre of the vertebra. With the ninth caudal vertebra these two perforating channels go to the central part of the vertebral body, which is now only a circular piece of 3-4'" in thickness, somewhat more truncated on the under margin, and somewhat sharper on the upper. After the fourteenth vertebra I can find no more perforations, the four last being very small and short nodules of decreasing size. All these, as far as the twelfth from behind, are enclosed in the axis of the caudal fin. The animal has ten pairs of ribs attached to the dorsal vertebrae. The first pair is short, only 2" 4'" long ; the largest ribs are from the fourth to the eighth, each of these is 6 inches; the last is 3" long. The first four pairs have double attachments, and are divided at the superior end into two prominent processes; the lower, being the ca-pitula costae, are attached to the body of the last cervical and three first dorsal vertebrae; the upper are the tubercula costae, of broader but shorter extent, and attached only to the transverse processes of the first four dorsal vertebrae. All the other ribs have only a single superior dilatation attached to the transverse process, and corresponding to the tuberculum of the former. At the lower end the ribs are somewhat broader, and truncated, and united by a small cylindrical sterno-costal bone with the breast-bone or sternum. This bone is composed of two distinct pieces, the anterior of broad subtriangular figure, the hinder smaller and oblong. To the very prominent parts under the fore edges of the first is attached the first pair of ribs, and near the posterior retracted edge the second pair. The second oblong piece of the breast-bone is united by a cartilaginous substance with the first, and bears also on each side two pairs of ribs, being united with them by sterno-costal bones. The first of these bones is broad and flat, and 7 lines long; the others more cylindrical, thinner, and longer, the fourth being 1" 10'" long. The fifth and sixth ribs have also sterno-costal bones, united to the end of the sternum by elastic substance; but the hinder ribs have only a short incurved conical cartilaginous epiphysis. The bones of the anterior members or breast-fins are of the common cetaceous form. The scapula is triangular, with a curved superior margin, 3^ inches long, and has two large anterior processes above the glenoid cavity, the superior or acromion being 1 inch long, and the inferior or coracoid process | inch. In the upper arm is a very strong bone, 1|" long; and in the forearm the two usual bones of nearly equal size, the hinder or ulnar bone being somewhat more prominent at both ends. The whole carpus is cartilaginous, but includes four very small spherical bones, of which the largest, like a pea, is situated in front of the junction of the radius with the ulna, and the smallest, like a small shot, before the thumb. The two others are placed between the connexions of the second, third, and fourth metacarpal bones. These bones are tolerably strong; but the same bone of the thumb or first finger is extremely small, and en- |