OCR Text |
Show 1881.] ANATOMY OF THE JAgANAS. 643 Pigeons, Plovers, and their allies (the " Charadriiformes" of Garrod') only amongst Homalogonatous birds. There are well-developed basipterygoid processes, which are always absent in the Rails, though of very frequent occurrence amongst the " Pluviales," occurring in all the Charadriinae and Scolopacinae I have examined. In Parra jacana and Metopidius albinucha, the long, narrow, slightly decurved vomer is emarginate apically, as in certain Cha- Fig. 1. Skull of Parra jacana, from below ; natural size. radriidae2 (see fig. 1). In the Rallidae it is, I believe, always sharp at the point. The maxillo-palatine processes are rather slender and directed backwards ; they have the form of concavo-convex lamellae, are not at all swollen, and do not unite by some way in the middle line, the vomer appearing between and (when the skull is viewed from the palatal aspect) below them. There is no ossified internasal septum, nor any ossification of the narial cartilages. The lacrymal is small, ankylosed with the nasofrontal region of the skull above, and with the " pars plana " below. On the posterior aspect of the skull there are no traces of the occipital fontanelles, which are found in so many of the birds related to the Plovers. The supraorbital impressions for the nasal glands, which are so conspicuous in most Plovers, the Gulls, Auks, and many other birds, are absent in the Pai*ridae. The combinations depending on the presence or absence of basipterygoid processes, of occipital foramina, and of impressions on the top of the skull for the supraorbital glands, coincide, as may be seen from the following table, pretty accurately, with hardly an exception, with the chief groups of the Pluviales (the web-footed Laridae and Alcidae being omitted as irrelevant to our present purpose) as determined by other characters. In the Table + and - represent respectively the presence or absence of the structure indicated. In the Plataleidae and Gruidae the nasal glands occupy the truncated edge of the cranium above the orbits, and hardly appear on its upper surface: this condition I have indicated by the use of the double sign (±). 1 P. Z. S. 1874, p. 117. 2 Cf. Garrod, P. Z. S. 1877, p. 417, figs. 2-4. |