chap, in.] VERTEBRAE AND RIBS: MAN. 109 



that the variation is more common on both sides than on one side ; 

 secondly, that it is not in its lowest development that it is most fre- 

 quent, but rather in a condition of moderate completeness, having 

 the proper parts of a true rib. 



(b) From dorsal towards cervical type. 



14. Reduction of ribs in the first dorsal is described by Struthers 

 in a specimen in the Path. Mus. of Vienna. " The whole of the 

 cervical vertebrae being present 1 there is no doubt as to the case 

 being one of imperfect first rib. On left side rib goes about § 

 round, and articulates with a process of the second rib. On right 

 side it joins second rib at from -J- to 1 inch beyond tubercle, but 

 again projects as a curved process where the subclavian artery has 

 passed over it. The manubrium sterni first receives a broad car- 

 tilage, as if from one rib only, and secondly a cartilage at the junc- 

 tion of the manubrium and body which is the cartilage of the third 

 thoracic rib." Struthers, J. Anat. Phi/s., 1875, p. 47, Note. (See 

 also Nos. 24 and 25.) 



(2) Homoeosis betiveen dorsal and lumbar vertebras. 



15. (a) From dorsal towards lumbar type. The characters chiefly 

 distinguishing dorsal vertebras from lumbars are the presence of 

 ribs attached to the former, and of long, flat transverse processes in 

 the latter. Secondly, the articular processes of lumbar vertebrae 

 generally differ from those of most of the dorsal series, each pair of 

 articular surfaces facing inwards and outwards respectively instead 

 of upwards and downwards as they do in the dorsal region. The 

 transition from the one type of process to the other, in passing down 

 the column, is generally an abrupt and not a gradual one. In Man 

 it occurs between the 12th dorsal and 1st lumbar, but in most 

 Mammals it takes place more or less in front of the last dorsal. 

 leaving several dorsal vertebrae with articular processes of the 

 lumbar type. (Struthers, /. c, p. 59.) 



Cases of rudimentary 12th rib in Man are not rare. When the 

 last dorsal in this respect approaches to the lumbar type, the 

 change of the articular process from dorsal to lumbar may take 

 place higher than normally, as in Struthers' Cases 1 and 2 (/. c. 

 p. 54 and p. 57). In both of these the change was symmetrical, 

 and in the first case it was abrupt and completed between the 11th 

 and 12th dorsals, but in the second it was less complete. Though 

 the place at which the change of articular processes takes place 

 here varies in correlation with the diminution of the last ribs, bo1 li 

 being higher than usual, such correlation is not always found, 

 change in respect of either of those characters sometimes occurring 

 alone. 



1 Struthers points out that unless the cervical vertebras above the rudimentary 

 ribs are counted there can be no certainty that in any given case these ribs are not 

 extra cervical ribs. 



