Description of the skeleton of Inia geoffrensis and of the skull of Pontoporia blainvillii, with remarks on the systematic position of these animals in the order Cetacea / by William Henry Flower.

  • Flower, William Henry, 1831-1899.
Date:
1866
Catalogue details

Licence: Public Domain Mark

Credit: Description of the skeleton of Inia geoffrensis and of the skull of Pontoporia blainvillii, with remarks on the systematic position of these animals in the order Cetacea / by William Henry Flower. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    outer wall of the nasal passage, but not entering in the slightest degree into the com- position of the free surface of the bony palate. In this disposition of the palatine and pterygoid bones Platanista stands alone among Cetaceans; even Inia presents no approximation to it. There are, however, in the latter genus some peculiarities in this region by which it may be distinguished from the ordinary Dolphins. Behind the posterior pair of teeth the palate loses its flatness, and begins to rise to a ridge in the middle line and slope away at the sides towards the roof of the orbits. The summit of the ridge is formed by the vomer, which is quite uncovered in the middle line by the palate-bones. The inner edges of these bones, applied to the surface of the vomer, are distinctly marked, and posteriorly are *4 distant from each other. The suture between them and the maxillaries is completely obliterated, so that their limits forwards and outwards cannot be definitely stated. As in the ordinary Dolphins, the palatines have each an outstanding, nearly vertical, plate running outwards and backwards, unattached posteriorly, and forming the upper part (in the natural position of the skull) of the outer wall of the chamber which lodges the great post- palatine air-sinus. This plate is slightly developed and very thin, perforated by numerous large lacunae, and, owing to the non-development of the outer reflected portion of the pterygoids, is completely free along its inferior edge. The pterygoids are comparatively simple, and also very thin and lacunated. As usual, the upper or attached portion forms a ridge along the side of the cranium, continuous posteriorly with the ridge on the side of the basisphenoid, which forms the inner wall of the cavity for the lodgment of the ear-bones. This portion articulates by nearly the whole of its inner edge with the hinder expanded part of the vomer, and externally with the alisphenoid and orbitosphenoid. From its anterior part springs the recurved descending plate which bounds externally the posterior nares, and, then turning inwards and backwards, forms the anterior wall of these passages below the palatines. This last-named plate of the pterygoid forms the hinder part of the bony palate; anteriorly it lies on the hinder free edge of the inferior surface of the vomer, but does not quite cover it to the middle line; behind the vomer it diverges rather more from its fellow, leaving a gap of from T to *2 in breadth. Posteriorly each terminates by a concave free margin. The third portion of the pterygoid, which exists in all ordinary Dolphins (excluding the Physeteridce), and which when present completely conceals that last described, being reflected from its hinder and inner edge outwards and upwards to meet the edge of the projecting plate of the palatine, and so close in the postpalatine sinus below, is wanting in Inia, or only represented in the osseous cranium by some small irregular body-excrescences. The result is that the cavity for the sinus is widely open below. It might be conjectured that this plate, being thin, brittle, and much exposed to injury during the process of cleaning the skull, had been broken away. It is certainly possible that such is the case;