110 MEMSTIC VARIATION. [part i. 



(b) From lumbar towards dorsal type. 



16. The formation of moveable ribs upon vertebrae normally be- 

 longing to the lumbar groups is in Man rarer than reduction of the 

 12th ribs. In these cases the ribs may or may not coexist with 

 transverse processes of considerable size. In a case of 13th rib in 

 Man, given by Struthers (I. c, p. 60), the change of articular pro- 

 cesses occurred a space lower than usual, being thus correlated with 

 the appearance of ribs at a lower point. 



(3) and (4). Homoeosis between lumbar, sacral and coccygeal 



vertebrae. 



17. The differences between the vertebrae of these regions are far 

 more matters of degree than those between the members of other 

 vertebral regions. By detachment of the 1st sacral (25th vertebra) 

 the lumbars may become 6, and in this case the 2nd sacral wholly 

 or partially takes the characters proper to the 1st sacral, but this 

 change is not necessarily accompanied by union between the last 

 sacral and the 1st coccygeal (see, for example, Struthers, I.e., 

 p. 68). On the other hand, the last lumbar may unite with the 

 1st sacral, and such union may be either symmetrical or unilateral 

 only. The amount to which the ilium articulates with these ver- 

 tebrae and the degree to which their processes are developed to 

 support it also present many shades of variation. Similarly the 

 last sacral may be free, or the 1st coccygeal may be united to the 

 sacrum. 



Since all these changes are manifestly questions of degree it 

 would be interesting to know whether any particular positions in 

 the series of changes are found more frequently than others, but I 

 know no body of statistics from which this might be determined. 

 In the absence of such determination there is no reason to suppose 

 the existence of Discontinuity in these variations. 



Homceotic Variation, Vertebrae and Ribs. 



II. More Complex Cases. — Man. 



From examples of the occurrence of Homoeosis between mem- 

 bers of the several regions we have now to pass to the more 

 interesting question of the degree to which Homoeosis in one part 

 of the column may be correlated with similar Homceotic variation 

 in the other parts. For, though each of the particular changes in 

 the various regions may occur without correlated change in other 

 regions, such correlation nevertheless often occurs, and in any con- 

 sideration of magnitude of Variation it is a factor of importance. 

 In several of the examples to be given it will be seen that the re- 

 distribution of regions is also associated with Meristic change in 

 the total number of segments in the column. It is obvious that in 



