THE EIBS, THE STEENUM, AND THE THOEAX 149 



straight or faintly emarginate. Each lateral surface presents at the 

 cephalic and caudal ends a dorsal and a ventral tubercle, separated by 

 a narrow longitudinal groove. To these tubercles, which are well 

 developed in old animals, is attached the bifurcated sternal end of a 

 costal cartilage. Between the two sets of tubercles the lateral surface 

 is gently concave along its cephalo-caudal diameter, and, for the most 

 part, dorso-ventrally flat. 



The dorsal and ventral surfaces closely resemble each other, and 

 also resemble the lateral surfaces. Thev differ from the lateral surfaces 



*/ 



usually in being narrower and 



more or less constricted in FlG - 11- 



the middle, and in not pos- 

 sessing the cephalic and 

 caudal tubercles. The ven- 

 tral surface (Fig. 100) is 

 narrower and more convex 

 at the cephalic than at the 

 caudal end, while in the 



dorsal surface (Fig. 101) the two ends are more nearly equal, although 

 the caudal always exceeds the cephalic. 



The First Stern ebra (Fig. 102) is called the manubrium 1 or pre- 

 sternum. It is nearly twice as long as the average sternebra, and, 



^ Cephalic End. 



Tubercles. 



Dorsal Surface. 



Left Lateral Surface. 



Caudal Surface. 



TYPICAL STERNEBRA, DORSAL VIEW. 



Costal Tubercle. 

 Dorsal Surface. - 



Groove. 



Omtal Tubercle. 



Eight Lateral Surface. 



Caudal Surface. 



MANUBRIUM OF STERNUM. VIEWED FROM ABOVE, BEHIND, AND THE 



RIGHT SIDE. 



although a little higher, it is much narrower. Its cephalic end is 

 compressed from side to side and rounded at the tip. The ventral 

 surface (Fig. 99) is raised in the middle line into a rounded keel. A 

 little cephalic to the middle each lateral surface is prolonged into a 



1 A handle. 



