53 



nerve and vessels. The vertebral ribs are convex upon both outer and inner sur- 

 faces, and maintain a nearly uniform breadth. The sternal ribs, or ossified car- 

 tilages, have a very irregular form . they are expanded and compressed, with the 

 margins directed forwards and backwards, where they join the vertebral ribs ; 

 they then contract as they approach the sternum, become compressed in an oppo- 

 site direction, having their thick and flattened margins looking outwards and 

 inwards, with the intervening sides deeply concave, and divided by strong ridges 

 from the margins. The extremity which joins the sternum is dilated and convex : 

 it presents two distinct articular surfaces, one on the inner or back part of the 

 rib*, adapted to the flattened posterior plate of the sternumf ; the other surface 

 is terminal!, and is applied to the anterior cubical processes of the sternum § : 

 each surface is divided into two compartments corresponding to the adjoining 

 surfaces of the contiguous sternal bones, to the interspace of which the sternal 

 rib is articulated. The eighth broad sternal rib presents a short thick elliptical 

 process on its anterior margin, midway between its two extremities ; this pro- 

 cess supports a flat articular surface for the contiguous sternal rib. 



'8ternum\\. — The form and construction of the assemblage of bones, called 

 collectively the sternum, are satisfactorily shown by a considerable proportion 

 in perfect preservation, including the manubrium and five consecutive pieces, 

 and a more posterior piece, probably the eighth of the sternal series. The 

 manubrium is the broadest as well as the longest piece ; the second bone is the 

 narrowest : beyond this they gradually expand to the sixth, which again con- 

 tracts ; the eighth is narrower than this, but broader than the second. It is 

 probable that three-fourths of the sternum are here present. 



The manubrium^ is an elongated, hexagonal, subdepressed bone ; the outer 

 or under side is convex transversely, and also longitudinally at its anterior half, 

 then concave to near its posterior part, which is crossed by a strong transverse 

 ridge, contracting backwards to a thick square process, standing boldly out from 

 the broader body of the bone, and with its posterior angles truncated to form two 

 articular surfaces for the second pair of sternal ribs**. The inner or upper sur- 

 face of the manubrium is convex transversely at its anterior third part, which is 



• PI. IX. fig. 5. i, J'. t Fig. 4. b, b' . J Fig. 5. a, a'. 



§ Fig. 4. a, a. « PI. IX. f Fig. 1. I. and fig. 2. ** Fig. 2. c. 



