MERISTIC VARIATION 4! 



2. Dorsal resembling cervical: forward homoeosis. Not so 

 common as above, but Struthers 1 describes a specimen in which 

 the first pair of ribs is defective. On the left side the rib 

 extends but two fifths of the way around, where it articulates 

 with a process on the second rib. On the right side it joins the 

 second rib about one inch beyond the tubercle. As seven nor- 

 mal cervical vertebrae are present in this specimen, it is to be 

 regarded as a modified dorsal rather than an extra cervical assum- 

 ing the characters of the dorsal, as in the preceding cases. 



3. Dorsal resembling lumbar. Frequently the twelfth rib 

 in man is rudimentary, in which case the last dorsal vertebra 

 assumes the form and general appearance of a lumbar. 



4. Lumbar resembling dorsal. Cases of a thirteenth rib are 

 not unknown but are more rare than the reduction of the 

 twelfth. 



5. Homceosis between lumbar, sacral, and coccygeal. The last 

 lumbar may unite on one or both sides with the sacral, in which 

 case the lumbar develops processes to assist in the support of 

 the ilium. On the contrary, the first sacral may remain detached, 

 thus becoming practically a lumbar. Similar relations obtain be- 

 tween the sacral and the coccygeal. 



A careful study of this whole subject develops the following 

 facts : 



1. That an increase in the number of parts in one region may 

 or may not affect the total number in the series. 



2. That consequently a change in number in one region may 

 or may not be accompanied by changes in other regions of the 

 same series ; that is, changes in the dorsal do not imply changes 

 in either the cervical or the lumbar. 



3. That homoeosis in vertebrae and ribs is confined to members 

 contiguous ; that is, if a cervical resemble a dorsal, it will be that 

 cervical lying next to the dorsal series. 



4. That the tendency is for an extra member to resemble 

 somewhat the members of the next region ; that is, an extra 

 dorsal is likely to resemble a lumbar or a cervical, if not to 

 entirely replace it, suggesting that it arose at the end, and not 

 in the middle, of the dorsal series. 



1 Bateson. Materials, etc., p. 109. 



