173 



The fourteen ribs which follow are all slender and rod-like.. 

 Besides the first, the sternal attachment of which has been 

 described, six other ribs join the sternum by means of sternal 

 ribs, which meet the points of junction of the segments of the 

 mesosternum, the union of the second rib being at the meeting 

 of the first and second segment, and so on. 



The costal cartilage of each succeeding rib, does not directly 

 meet the sternum, but joins that of its j^redecessor. 



The sternal ribs, in the case of the fourth, fifth, sixth and seventh, 

 are not completely ossified in their outer segments ; thus, there 

 intervenes between the end of the vertebral rib and the ossified 

 part of the sternal rib adjacent to the sternum, an intermediate 

 cartilaginous segment. (PI. YIL, fig. 5 xxxx). These cartilaginous 

 parts of the sternal ribs are not, however, completely segmented off 

 from the inner ossified parts ; the failure in ossification is gradual, 

 and the ossification, complete in the sternal extremity, becomes 

 less and less complete in the outer segment, till eventually cartilage 

 only stands in place of bone. The junction between the cartilag- 

 inous segment of the sternal rib and the vertebral rib is quite 

 abrupt. 



The heads of the ribs, other than that of the first, are articu- 

 lated with the bodies of the vertebrae, as mentioned in the de- 

 scription of the spinal column ; thus the head of the second rib abuts 

 on the bodies of the eighth and ninth vertebra3, and so on. Following 

 the first, the part in the other ribs corresponding to the tubercle is 

 attached to the transverse processes by ligamentous union, which 

 is close and intricate as far as the eleventh ; in the remainder, the 

 union is less close, as the transverse processes gradually diminish 

 in prominence. As already described, the transverse process of 

 the eighth vertebra is distinctly facetted for part of the articula- 

 tion of the head of the first rib ; that of the ninth is only imper- 

 fectly so, but beyond this no definite facets are evident, but 

 merely roughened surfaces for the ligaments. 



THE STERNUM. 



(PI. VIL, figs. 5, 6, 7 and 8). 

 The sternum consists of a presternum, a mesosternum of six 

 segments, and a ziphisternum. The presternum is i-emark- 

 able on account of its strong and prominent keel, which projects 

 downwards and forwards to an extent which is greater than its 

 length in a fore and aft direction (fig. 6/j. The lateral wings, 

 which are slightly concave on each side of the keel, articulate (or 

 ankylose) with the first rib, as described under tliat head, the pos- 

 terior end of the junction coming right up to, or even encroaching 

 upon the concave articular facet on its liinder face for the first 

 segment of the mesosternum. The inner, or superior, surface of 



