AXIAL SKELETON OF THE OSTEICH. 443 



The Seventh Rib. 



The seventh rib (fig. 75, vii & vii') is attached to the twenty-fourth vertebra. In 

 spite of its being much more bent, it is decidedly shorter (by nearly the length of its 

 tuberculum) than the sixth rib, though it is longer than the fourth rib when measured 

 along its convexity (fig. 1, vii). 



The capitulum and tuberculum diverge at an angle of about 80°. The pneumatic 

 foramen (vii',/") is still larger, forming quite a chasm. The articular surface for the 

 diapophysis is also rather larger (vii', t). 



The shaft of the rib is more rounded and slender generally, especially towards its 

 distal part, which, however, expands towards its extremity so largely as to about equal 

 in size the distal end of the sixth rib. It articulates at its distal end with the fifth 

 sternal rib. 



The shaft is also bent, with a decided or slight sigmoid flexure, convex postaxially at 

 its more proximal part, and convex preaxially at its more distal part ; but it may only 

 show a preaxial concavity and a postaxial convexity. 



The ridge traversing the outside of the root of the capitulum is still more marked. 



There appears to be generally no rudiment even of an uncinate process, but it may be 

 developed, though always to a less extent than in the seventh rib. 



- The Eighth Rib. 



This rib (attached to the twenty-fifth vertebra) is smaller in all dimensions (fig. 75, vili) 

 than the seventh rib, and in length is intermediate between the third and the fourth ribs. 



It closely resembles in shape the seventh rib ; but the capitulum is rather less long 

 compared with the tuberculum ; the pneumatic foramen is smaller ; but there are 

 small openings on the postaxial or inner surface of the tuberculum. The articular 

 surface for the diapophysis is smaller and nearly flat. 



The shaft of the bone is more or less bent ; it may exhibit a rudiment of an uncinate 

 process. It articulates at its ventral end with the sixth sternal rib (fig. 1, viii). 



The Ninth Rib. 



The ninth rib (attached to the twenty-sixth vertebra) is much shorter, about the same 

 length as the third, and, like the latter, ends freely at its distal end (fig. 75, ix). It is 

 much more slender than any other rib. Compared with the eighth rib, the capitulum 

 is again shorter relatively, exceeding the tuberculum less in proportion. The pneumatic 

 foramen on the margin of the neck is minute ; but there is a large aperture on the post- 

 axial aspect of the tuberculum, where the capitulum joins it. The shaft of the bone is 

 again straighter (fig. 1, ix). 



The ninth rib may have at its ventral end an extremely long, slender, curved bone 

 applied by its other extremity to the outer or ventral side of the sixth^itemal rib. 



3q2 



