522 Zoological Society. 



each rib, and are about 5 lines broad at their origin : towards their 

 termination they spread laterally to the width of 1 inch. As they 

 approach the lower rib they get gradually thinner. In the first and 

 last rib they are totally wanting. The last rib, at its centre, has a 

 surface concave externally, produced by the action of the thigh. 

 The stemo-costal bones are seven in number ; the last one curved 

 suddenly at its costal end. 



" The body of the sternum is long. The keel is much developed 

 at its top, and forms a very acute angle posteriorly, terminated by 

 a small line. The space for the attachment of the middle pectoral 

 muscle is considerably larger than that for the attachment of the 

 great pectoral. On each side of the keel there is a large space, ter- 

 minating inferiorly in one, owing to the shortness of the middle 

 layer compared with the lateral ones. The keel terminates abruptly 

 inferiorly. The ensiform process has a ridge in the middle, along 

 which and the inferior edge of the keel a membrane was attached 

 (which separated in maceration). The external layers of the bone 

 are, as has been already incidentally noticed, much longer than the 

 middle one : they curve inwards toward each other, and are tipped 

 with cartilage. The sternal Jbssa is large and very distinct. The 

 sternal apophyses are very large. 



" The coracoid bones are long, strongly formed, and smooth an- 

 teriorly ; the\nargin much produced at the superior internal edge, 

 and the ends furnished with long hamuliform processes, extending 

 upwards and downwards. The superior one is attached to the cla- 

 vicle by the intervention of ligament. The upper part of the os 

 coracoides is bent upon itself at an angle greater than a right angle. 

 They are larger at their inferior ends, the inner ends being pro- 

 duced and curved forwards. The glenoid cavity of the bone is 

 situated on the exterior posterior part, and is formed by this bone 

 and the scapula, about three fifths of the cavity being formed by the 

 os coracoides. 



" Each clavicle is turned downwards, and is broader near the 

 coracoid bone, and tapering to the front, where there is a protu- 

 berance formed by the junction of the clavicles : this protuberance 

 does not touch the sternum. Posteriorly they give off a flat conical 

 process, which goes down internally to the coracoid bone, and is 

 united to the process situated on the posterior part of the scapula, 

 immediately inferior to its head. 



" The scapula is remarkably broad and thin : its neck and head 

 rounded. There are three articulating processes in this bone : one 

 with the furculum ; another with the coracoid bone; and the third 

 with the humerus. 



" On comparing the sternum and adjacent bones with the sterna 

 of some nearly allied Birds, we find less development of the keel 

 in the Loony and less development of the lateral wings in the 

 Auk, and more in the Spheniscus. The differences will be best shown 

 by the following tables : 



