1868.] PROF. HUXLKY ON THE ALECTOROMORPH^. 30/ 



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 (ajiart 

 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 manu- 

 brium 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 i'rom the INIusopha- 

 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 Bidus. 



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 hypo- 

 cleidium is as completely ankylosed with the manubrium. In the 

 ankylosis of the furcula with the manubrium, Ojnsfhocomus 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 Meleayris. 



The scapula has a long and strong acromial process, which ex- 

 tends forwards to the clavicle (with which it is not ankylosed), and 

 forms the entire inner boundary of t)ie large canal for the tendon of 

 the middle pectoral muscle. 



The acromial process is very small in the AlectoromorphcB, but 



