108 MERISTIC VARIATION. [part i. 



13. Cases of the development of ribs on the 6th cervical seem 

 to be extremely rare. One is given by Struthers in a young 

 spine, set. 4. The ribs were present as rudiments only, being 

 the same on both sides in the 6th vertebra, and on the left side 

 in the 7th. Each of these rib-elements was -^ inch long. In the 

 6th the ribs rested on the body of the vertebra, but in the 7th the 

 rib did not reach so far. Full details, q. v., Struthers, J. Anat. 

 Phys., 1875, p. 32. 



Cervical ribs on the 7th vertebra are comparatively common, 

 being sometimes moveable and sometimes fixed. The literature of 

 this subject up to 1868 is fully analyzed by Wenzel Gruber, 

 Mem. Ac. Sci. Pet, Ser. vn. T. xiil, 1860, No. 2, who refers to 76 

 cases of such ribs, occurring in 45 bodies, being all that were known 

 to him in literature or seen by himself. In addition to these 12 

 cases are described (10 in detail) by Struthers (I. c.\. Some of 

 the results of an analysis of these cases are important to the study 

 of Variation. 



Of 57 cases, the ribs were present on both sides in 42 cases 

 and on one side only in 15. 



According to the degree of completeness with which the cervi- 

 cal ribs are developed, Gruber divided them into four classes \ 



1. Lowest development. Cervical rib not reaching beyond the 

 transverse process ; corresponding to the vertebral end of a true 

 rib with capitulum and tnberculum, and articulating by both of 

 them. Rare form. 



2. Higher development. Cervical rib reaching beyond the 

 transverse process for a greater or less extent, either ending freely 

 or joining with the first true rib. Commonest form. 



3. Still higher development. Cervical rib reaching still further, 

 and joining the cartilage of the first true rib either by its cartila- 

 ginous end or by a ligament continued from this. Hardest form. 



4. Complete development. Cervical rib resembling a true rib, 

 having a cartilage (generally for a greater or less part of its length 

 united with the cartilage of the first true rib) connecting it with 

 the sternum. Less rare form. 



Gruber states, as the result of an analysis of 47 cases, that the 

 third of these states is very rare, that the second condition is the 

 common one, and that the fourth or complete condition is commoner 

 than the first or least state of development, which is also rare. 

 Of Struthers' cases the majority seem to belong to Gruber's second 

 class, while that on the left side in Struthers' Case 4 must have 

 approached Class 1, and that on the left side in Case 10 belonged 

 to Class 3. 



Two features in this evidence are of especial consequence : first 



1 Gruber considered that cervical ribs in Man are probably of two kinds, the 

 one arising by development of an "epiphysis" on the superior transverse process, 

 and the other by development of the "rib-rudiment" contained in the inferior 

 transverse process. It is of cases of the latter kind that he is here speaking. 



