84 FRANK BLAIR HANSON # 



affected in length or shape. Advocates of a costal origin for the 

 sternum derive the xiphisternum from the ends of the seventh 

 or eighth ribs or both. However, when these are absent, the 

 formation of the xiphisternum does not seem to be affected in 

 the least. As in the reptiles, it is a constant feature regardless of 

 the absence or presence of ribs. 



In the work of Paterson ('09) and Lickley ('04) an even more 

 suggestive fact is clearly apparent. This relates to the tendency 

 of ribs to grow to the ventral side and fuse as was also seen in 

 Chamaeleo and noted in the discussion of reptiles. In man the 

 seventh rib normally reaches the sternum, but in its mode of 

 attachment we have the remarkable statement of Lickley that 

 in over 50 per cent the seventh costal cartilages are either 

 fused or articulate with each other in a plane anterior (ventral) 

 to the xiphisternum. That is to say, these ribs which are anterior 

 to the posterior end of the sternum reach the median line and fuse 

 just as did the ribs posterior to the posterior end of the sternum 

 in Chamaeleo. In all the accounts here under review the ribs 

 act as if entirely independent of and irresponsible for the being 

 or well-being of the sternum. 



Paterson's results are not so striking in large percentages as 

 Lickley's, but sufficiently so to give us pause, even if considered 

 alone. He examined 236 human fetal sterna and found that the 

 seventh costal cartilages articulated in front of the sternum in 

 14.4 per cent. 



In •this connection three special cases may be cited, the first 

 two reported by Lickley and the last by Dwight : 



1. The sixth costal cartilages articulated dorsally with the 

 lower end of the mesosternum and ventrally with one another. 

 The seventh cartilages articulated with the lower borders of the 

 sixth cartilages and by their extremities with one another. 



2. Girl, eighteen years. Mesosternum terminated at level of 

 insertion of fifth ribs. The extremities of the sixth and seventh 

 cartilages on the left side were fused together, those on the right 

 were closely united by fibrous tissue. The two bars formed in 

 this way articulated with the mesosternum above, and with one 

 another in front. 



