OF COLYMBUS TORQUATUS. 



147 



The keel begins just posterior to the small manubrial process, with a very thick, stout 

 maroin which curves with a concave outline downwards and greatly forwards ; so that the 

 apex of the keel, which is quite acute, projects much in front of the anterior border of the 

 sternum The crest of the keel is regularly a little convex for its anterior half; in 

 the rest of the length it is almost perfectly straight, to its subsidence into the level of the 

 surface of the bone, which takes place just at the base of the xiphoid. The crest of the 

 keel is broader than the vertical portion, and, with the latter, is rough for the attachment 

 of the pectoral muscles. The vertical depth of the keel is, just at its anterior extremity, 



01 Lilt: pcuiuiui ixi^v^^. - j. _ - -ill 



very considerable, being nearly one and a half inches; but very quickly, by the 



great 



Sternum and scapular arch in situ, lateral view, one half natural size. 

 (Figure 1.) 



Sternum and scapular arch in situ, from helow, one half natural size. 

 (Figure 2.) 



downward projection of the body of the bone, joined with the slight convexity of the crest 

 of the keel itself, it becomes inconsiderable, and then more gradually decreases as it pro- 

 ceeds backwards. „ 



Viewing, now, the sternum as a whole, we have to notice how great an extent of surface 

 is secured" with a trifling increase of weight. Posteriorly, this is attained by means of the 

 great lateral projection of the apophyses, as well as by their length, and by the breadth and 

 projection backwards of the thin, almost cartilaginous xiphoid. Anterior y, where the 

 sternum is not so wide, the deficiency is atoned for by the great depth of the keel, and 



MEMOIRS BOST. SOC. NAT. HIST. Vol. I. Ft. 2. 



38 



