464 The American Naturalist. [June, 



sumably in the pro-anthropos, there are thirteen complete ribs 

 and four lumbar vertebrae, while man has twelve ribs and five 

 lumbars. Thus we may consider the superior lumbar of 

 adult man as a ribless dorsal ; not so in the human embryo, 

 however, for Rosenberg 1 has found a cartilaginous rudiment of 

 the missing 13th rib upon the so-called first lumbar. Atavism 

 contributes an earlier chapter in the history of this region, for 

 Birmingham 2 reports, out of fifty cases examined in one year, 

 two in which there were six lumbars, and in each the 13th 

 rib was well developed; this is an interesting example of 

 "correlated reversion," for as the pelvis shifted downward to 

 its ancestral position upon the 26th vertebra the 13th rib was 

 also restored. The other ribs are in what the ancients styled 

 a " state of flux ; " our 8th rib has been so recently floated 

 from the sternum that, and according to Cunningham, 3 it 

 reverts as a true rib in twenty cases out of a hundred, showing 

 a decided preference for the right side. Regarding also the 

 occasional fusion of the 5th lumbar with the sacrum and the 

 unstable condition of the 12th rib, which is, by variation rudi- 

 mentary or absent, Rosenberg makes bold to predict that in 

 the man of the future the pelvis will shift another step 

 upward to the 24th vertebra and we shall then lose our 12th 

 rib. The upright position and consequent transfer of the 

 weight of the abdominal viscera to the pelvis may be consid- 

 ered the habit associated with this reduction of the chest; at 

 all events, in the evolution of quadrupeds there is a constant 

 relation of increase between the size of the posterior ribs and 

 the weight of the viscera, until the rib-bearing vertebra rise 

 to twenty and the lumbars are reduced to three. 4 It would be 

 interesting to note the condition of the ribs in some of the 

 large-bellied tribes of Africans in reference to this point. 



The coccyx has naturally been the center of active search 

 for the missing flexible caudals. As is well known, the adult 

 coccyx contains but from three to five centers, while the 

 embryo contains from five to six. Dr. Max Bartels has made 

 " Die geschwanzten Menschen " the subject of an exhaustive 



'Journal of Anatomy and Physiology, 1891, p. 526. 



