20 THE VOYAGE OF H.M.S. CHALLENGER. 



lost sight of, aud, lying as it does iu tlie substance of the abdominal muscles, unless 

 specially looked for, is apt to be omitted in the enumeration of the ribs. 



The first vertebral rib in Eudyptes chrysocome measures only one inch iu length. It 

 is, however, provided with a well-developed head, neck and tubercle, by means of 

 which it articulates with the body and transverse process of the first dorsal vertebra. 

 Its inferior extremity terminates in a sharp point, which lies embedded in the substance 

 of the scalene muscle. This rib has no connection with the sternum, being destitute of 

 any sternal segment. It is also destitute of an uncinate process. 



The second vertebral rib is also destitute of a sternal segment, and consequently does 

 not articulate with the sternum. It is about three times as long as the first rib, from 

 which it differs, inasmuch as it develops an uncinate process. 



The following ribs as far as the seventh are much flattened, and each bears a large 

 uncinate process. The eighth and ninth ribs, again, more nearly resemble the first and 

 second, inasmuch as they lose the flattened form, become almost cylindrical, and are much 

 more slender than those which precede them. The eighth is provided with an uncinate 

 process, which is wanting in the case of the ninth rib. The tenth rib, as already observed, 

 is rudimental, and does not articulate with the vertebral column as do aU the others, its 

 proximal extremity being attached by ligament to the middle in length of the posterior 

 border of the ninth vertebral rib. The tenth rib is, moreover, devoid of an uncinate 

 process. AU the vertebral ribs, with the exception of the first and second, possess 

 sternal segments. The tubercles of the eighth and ninth vertebral ribs come into relation 

 with the lower surface of the iliac bone, close to its anterior margin or crest. 



The uncinate processes are of exceptionally large size, and much flattened. They 

 are elongated-quadrilateral in form, and project backwards and upwards. They are met 

 with in every vertebral rib, with the exception of the first and the last two. In the case 

 of the anterior ribs they are attached to the junction of the middle and lower thirds 

 of the bone, but occupy a higher position with reference to the posterior ribs, being 

 attached in these to about the middle of their length or even opposite the junction of the 

 upper and middle thirds of their vertebral segments. They are of largest size about the 

 middle of the costal series. As is well known, iu all the Penguins the uncinate processes 

 are connected with the ribs by means of distinct synovial articulations, and never become 

 anchylosed with them as in the majority of birds. 



The sternal ribs are eight in number on each side, and belong to the vertebral 

 segments posterior to the second. They increase in length from the first to the sixth, all 

 of which articulate with special facets on the lateral margin of the sternum. The seventh 

 sternal rib (belonging to the ninth vertebral segment), is much more slender than those 

 which precede. It difi"ers from these inasmuch as it does not reach the border of the 

 sternum, but falling short of that bone is attached by ligament to the sternal segment 

 next in front, about a quarter of an inch from the margin of the sternum. The eighth 



