OCR Text |
Show 1868.] PROF. HUXLEY ON THE ALECTOROMORPHAE. 307 length of the whole sternum. There are no proper costal processes, the anterior lateral angle of the sternum being rounded off, in such a manner that the middle of the anterior edge of the sternum (apart from the manubrium) is far in advance of the antero-lateral angles. A straight, styliform, osseous process, compressed from side to side and continuous with a slight crest which runs for a short distance down the anterior face of the sternum, takes the place of both manubrium and hypocleidium, being continuous, on the one hand, with the sternum, and, on the other, with the furcula. The keel of the sternum is extraordinarily small and cut away in front, the angle formed by the union of the anterior and ventral margins being situated opposite the junction of the third and last fourths of the length of the bone. The anterior contour is at first concave, afterwards slightly convex. The ventral edge is at first concave and expanded from side to side, but afterwards becomes slightly convex. The sternal ribs are attached along the anterior half of the lateral contour of the sternum. The ridge which bounds the origin of the middle pectoral muscle externally, extends from the outer end of the articular fossa for the coracoid to the summit of the inner notch, and thence a little way upon the middle xiphoid process. The surface left between this line and the attachment of the sternal ribs is extremely narrow. The form of sternum thus described appears to be altogether peculiar to Opisthocomus, and to be as remote from the Musopha-gine as it is from the Gallinaceous type. The carina is much what that of Crax would be if the anterior edge were further cut away; but it is still more like that of an un-hatched chick. The coracoids are similar to those of the Pigeons, and have very strong subclavicular processes. They are ankylosed with the clavicles - a rare peculiarity, which has been observed in Didus. The furcula is shaped like a fork with nearly straight tines, and is remarkably short, having not much more than the half the length of the coracoids. Its proximal ends are so completely ankylosed with the coracoids that no trace of the primitive distinctness of the bones is discernible; inferiorly, as has been mentioned, the straight hypocleidium is as completely ankylosed with the manubrium. In the ankylosis of the furcula with the manubrium, Opisthocomus stands alone. For, in the other birds (such as the Pelicans, Frigate-bird, Cranes, Balceniceps) which have the furcula united with the sternum, the ankylosis takes place between the furcula and the carina. Crax globicera has a remarkably short furcula, with a long straight hypocleidium ; and the furcula is almost as little curved, and has a no less straight hypocleidium, in Meleagris. The scapula has a long and strong acromial process, which extends forwards to the clavicle (with which it is not ankylosed), and forms the entire inner boundary of the large canal for the tendon of the middle pectoral muscle. The acromial process is very small in the Alectoromorphce, but |