263 



is eitlier fused with the first dorsal rib or articulates with it by means 

 of an intervening cartilage. 



The junction of the two bones occurs at the point where the sub- 

 clavian artery crossed the thoracic inlet. It is further to be noted 

 that these specimens do not present any particular marking which can 

 be associated with the passage of the nerve trunk. 



In all these cases the first dorsal rib exhibits the vein marking. 

 Thus in the type now under consideration the nerve influence on the 

 appearance of the bone has been at a minimum, while on the other 

 hand the vascular markings are well shown. It seems but logical 

 to consider that the artery in these cases has stood as causative factor 

 in the production of the skeletal condition. It is worthy of note in 

 reference to what I 

 have previously stated 

 regarding the more 

 intimate relation of 

 the left artery to its 

 rib (1) that of these 

 three instances, two 

 occurred on the left 

 side. 



A more complete 

 form of cervical rib is 

 shown in Fig. Y. Of 

 this type four instan- 

 ces in the present 

 series. 



The illustration 

 shows that v^hile both 

 artery and nerve have 



left an impression on its upper surface the rib is cut short immediately 

 in front of the insertion of scalenus anticus. In the specimen from 

 which the figure was taken the veins were very large. Although this 

 condition was caused by the presence of clot — an artefact due to 

 injection of the subject with formalin — it illustrates the point now 

 to be considered. In this subject the tip of the rudimentary rib was 

 connected with the sternum by a ligamentous band on the upper 

 aspect of which lay the sub-clavian vein. This occurred in two of 

 the four instances. Eegarding the other two I am unable to make any 



Fig. V. Seventh cervical vertebra and ribs. Case A. 

 English. Adult. Male. V> Nat. size. 



Presents cervical ribs whose ossification extends 

 as far forward as the crossing of the sub-clavian vein. 

 A common groove is shown for the nerve and artery. 

 Note the sigmoid, appearance of this groove which has 

 been described in a previous paper (4). 



