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Show 484 DR. H. BURMEISTER ON PONTOPORIA BLAINVILLII. [May 9, 4. Preliminary Observations on the Anatomy of Pontoporia blainvillii. By Dr. H . B U R M E I S T E R , F.M.Z.S. Some weeks ago one of my friends brought me the dry body of a specimen of Pontoporia blainvillii, which was taken living in the mouth of the River Guegueu Grande, in 38° 33' S. lat. The body had lost all the external flesh and the greater part of the viscera, and could only be made use of for a skeleton, which is now exhibited in the public museum of Buenos Ayres. As the internal structure of this interesting animal is entirely unknown, I beg leave to communicate to the Zoological Society my observations made during the examination of the body, some of them being very curious, and worthy, as I believe, to be known to science. I will not speak of the general figure of the animal and its colour, because most of the external surface was lost; but I may mention that another entirely well preserved individual in our museum has no trace of the white stripe on each side of the body which is represented in D'Orbigny's figure (Voyage, M a m m . pl. 23). The upper part of the whole body is blackish grey, and the whole underside white, which colour extends halfway up the sides, and occupies also the under jaw and the sides of the head. But the general figure of both animals is the same, and therefore I cannot doubt that m y species is the same as that figured by D'Orbigny. As the skull is already well known by the figure in the work above mentioned, I will not enter into a description of that part of the skeleton, especially since Mr. Flower, one of the best-informed observers of the skeletons of the Cetacea, is occupied with a comparative description of the skulls of Pontoporia and Lnia, the former sent by myself to Dr. J. E. Gray for the British Museum. I will therefore begin my description with the vertebral column, which is composed of forty-two vertebrae, divided into seven vertebras of the neck, ten of the back, seven of the lumbar portion, and eighteen of the tail, of which the first five are provided with inferior spines or hsemapophyses. The seven vertebrae of the neck are all free, and none of them anchylosed; they have together an extent of 1" 10'", each of the first two being 5'" long, and the five others 2g'". Only the second vertebra has a strong reclined spinous process, and very broad thick transverse processes ; the five following have no spinous processes, but transverse processes of different size and form. The transverse process of the third vertebra is somewhat larger than the same part of the fourth, and the fifth vertebra has the smallest transverse process of all; but on the lower margin of the body cf the same vertebra springs up another thick and short tubercle, which is already indicated on the fourth vertebra, and presents itself also on the two following. To this lower tubercle of the seventh cervical vertebra is attached the capitulum of the first rib. The ten dorsal vertebrae have together an extent of 6 inches, each one being somewhat longer than its predecessor; so that the first is |