OCR Text |
Show 426 PROF. HUXLEY ON THE CLASSIFICATION OF BIRDS. [Apr. 1 1, it receives the posterior extremities of the palatines and the anterior ends of the pterygoid bones, which thus are prevented, as in the Ratitae, from entering into any extensive articulation with the basisphenoidal rostrum. The basipterygoid processes spring from the body of the sphenoid, not from its rostrum, and they articulate with the pterygoids very near the distal, or outer, ends of the latter bones. The head of the quadrate bone is single, as in tbe Struthious birds (Parker, I. ci). But the sternum of Tinamus has a great crest, and the coracoid and scapulas have tbe arrangement and structure usual in the Carinatae. And though the ischium is not united with the ilium by bone behind the acetabulum, so that the sciatic notch is not converted into a foramen by bone, this character is not universal among the Ratitae, and, in Tinamus, a fibrous or cartilaginous bridge does connect the two bones. Though the most Struthious of all Carinate birds, then, Tinamus cannot, I think, be removed from the order of the Carinatae. II. In the large assemblage of birds belonging to the Cuvierian orders Gallinae, Grallae, and Natatores, which may be termed Schizognathous, the vomer, sometimes large and sometimes very small, always tapers to a point anteriorly; while posteriorly it embraces the basisphenoidal rostrum, between the palatines. But the latter bones and the pterygoids are directly articulated with one another and with the basisphenoidal rostrum, and are not borne by the divergent posterior ends of the vomer. The maxillo-palatines are usually elongated and lamellar; they pass inwards over the anterior processes of the palatine bones, with which they become united, and then bending backwards, along the inner edge of the palatines, leave a broader or a narrower fissure between themselves and the vomer, and do not unite with it or with one another. This Schizognathous arrangement of the palatine bones is extremely well displayed by the Plover, as the accompanying figure of the parts in Charadrius pluvialis shows. The palatine bone (fig. 6, Pl) presents an expanded part, which may be called its " body," the inner and outer edges of which are produced into internal and external " laminae," separated by a longitudinal groove or depression. In this bird the outer lamina descends much further than the inner. The free edge of the outer lamina joins the posterior margin nearly at a right angle, and thus gives rise to the "postero-external angle." The postero-internal angle of the body of the bone is produced into a "pterygoid process" which articulates with the pterygoid posteriorly, and with the basisphenoidal rostrum internally. Superiorly the body of the palatine bone passes into what may be termed its " ascending process," which bends round so as to form the posterior boundary of the nasal passage, and ends, on the inner side of that passage, in a slender prolongation which passes forwards and applies itself to one of the forks of the vomer (fig. 8, Vo). |