OCR Text |
Show 1904,] OSTEOLOGY OF THE EL0P1D.E AND ALfiULID.E. 51 from the ectosteal articular, and the articular facet for the head of the quadrate is formed in its upper part by the endosteal articular, and in its lower part by the combined angular and ectosteal articular. Hyopalatine Series (text-fig. 17, p. 50).-The hyomandibular articulates with the cranium by a single broad head, and its axis slopes downward and forward. Owing to the smallness of the gape the quadrate-articular joint is far in advance of the hyomandibular-cranial articulation, and the symplectic runs nearly horizontally forwards. The palatine cartilage ossifies at its anterior and posterior ends, but remains unossified for the greater portion of its length. The anterior head articulates with the mesethmoid, the posterior with the prefrontal. The ectosteal palatine is of small extent, and bears crowded, small, long, sharp teeth. It is united with the anterior of the endosteal palatines, but is remote from the posterior one. The hinder two-thirds of the palatine cartilage, and its posterior ossification, lie in a trough formed by the ectopterygoid and entopterygoid. The entopterygoid bears an elongated patch of hemispherical teeth similar to those on the parasphenoid; the ectopterygoid is toothless, or may bear two or three small teeth in continuation of the patch of teeth on the palatine. There is a prominent, externally-directed, horizontal process of the ectopterygoid, which serves to form part of the floor of the orbit. Its outer edge rests against the upper edge of two of the suborbital bones. Opercular Series (text-figs. 16 & 17, p. 50).-The subopercular is large. The branchiostegal rays are 15 in number; they all arise from the outer face of the hyoid arch. The first two lie freely in the branchiostegal membrane, the next ten are attached to the posterior two-thirds of the ceratohyal, and the last three are attached to the epihyal. They form a well-graduated series, those in front having the form of slender curved needles, the hinder ones being larger and lamellate. Hyobranchial Series (text-fig. 18, p. 52).-The upper and lower hypohyals are equal in size, although in an external view the lower appears to be the larger. The urohyal extends back a little beyond the posterior extremity of the third basibranchial. The gill-rakers are all short and stumpy. The interhyal is ossified. There is a conspicuous dentigerous membrane-bone covering the first second, and third basibranchials and the hinder part of the o-lossohyal. The teeth are hemispherical, and resemble those of the parasphenoid and entopterygoid, with which, in fact, they engage. The glossohyal is movable beneath this dentigerous plate, but the basibranchials are not. The body of the glossohyal consists of cartilage in front and cartilage-bone behind, and an edentulous thin membrane-bone covering both. There is a very small dentigerous bone covering that cartilage which represents the fourth and fifth basibranchials; the teeth of this are small and pointed, like those of the gill-rakers. The first pharyngobranchial is perfectly conformable with the second, and is set in a line with the first epibranchial. A true spicular bone appears to be wanting. The third pharyngp- |