NUMERICAL VARIATION IN THE HUMAN SPINE. 303 



free portion of the 24tli is generally a part of a good ultimate, and the 23d generally a 

 good penultimate. 



IV. When the 24:th is the fulcralis, certainly or probably, there is often a secondary 

 promontory below it. The 23d may be a good ultimate or a penultimate, or it may pre- 

 sent features of both. Thus the transverse processes may be thick and broad at the root, 

 like those of a oth lumbar, and toward the tips they may become light by the rising 

 of the lower border, as in the 4th lumbar. The 22d is never a typical penultimate. That 

 of spine 478 is the nearest approach I have seen. Perhaps the 1st coccygeal is more 

 likely to be fused to the sacrum if the 24th be the fulcralis or be much sacralized, but I 

 have great doubts whether its condition is of any value. 



In brief it appears that the spine adapts itself much more easily to an additional 

 praesacral vertebra than to the loss of one. In the former case, assuming that the 

 addition is in the thorax, the 24th vertebra is or may be a very good penultimate lumbar, 

 while in the opposite case it is not. Rosenberg alludes to a case of Tenchini, as possibly 

 presenting this condition. I have not had access to it. In my series there is no perfect 

 case. Both 478 and 267 approach the conchtion, and present lumbar regions which on 

 the whole are not far from typical, but the more normal condition of spine 7G4, in which 

 the 26th is the fulcralis, is evident. 



The Variations of the 19th and 20th Vertebrae. — These are familiar to all who have 

 studied this subject, but it may not be amiss to recapitulate some of them briefly. 



In Class I, Group A, the lUth in G-19 is thoracic, with one costal element free but 

 minute and the other fused like a transverse process; in 636 the 20th, as far as these 

 features are concerned, is much hke it; in 567 the 2()th, though in most resjjects lumbar, 

 bears ribs. In Group B, both in 729 and 306, the change of articular processes is above 

 the 19th ; the former seems to have transverse processes cut through at their bases, and 

 the latter small ribs that have become fused so as closely to resemble transverse processes. 



In Class II, in wliicli the 2'jth vertebra is more or less sacralized, we find in 561 that 

 the 20th is thoracic with lumbar-like transverse processes; that it is more lumbar in 361; 

 that in X it is more transitional and hard to place, suggesting a diiferent interpretation 

 for the two sides; that in G-22, though rather transitional in some respects, the 13th ribs 

 are typical last ones ; and that in 2, though on the whole lumbar, it has free transverse 

 elements. 



In Class III, in which there are 25 free praesacrals, the 20th is held to be thoracic 

 in Group A, and lumbar in Group B, but still in the development of the costal ele- 

 ments, the nature of the spinous process, and the place of change of the articular proc- 

 esses, there is absolutely no rule. 



