262 



The nerves pursued a more forward course than usual and thus the 

 part of the rib is left complete which represents the bone proximal 

 to the point where the plexus passed across it. The growth of the 

 portion distal to this point has been completely inhibited. 



But the level of the crossing of the costal arch by the nerve 

 trunk cannot be held to indicate that of either artery or vein. Variations 

 in the constitution or arrangement of the brachial plexus may free the 

 rib from the influence of the nerve or it may at most exhibit merely 

 a deep groove for this structure. 



Fiff. III. 



Fig. IV. 

 Case B. 



English. 



Fig. III. Seventh cervical vertebra and rib, right side. 

 Adult. Male. V^ Nat. size. 



Illustrates type of rib which is ossified only as fai- as the crossing of the 

 lowest brachial nerve trunk. In the recent state no ligamentous connection with 

 the sternum was present. 



Fig. IV. Seventh cervical rib, left side 'showing articulation with first dorsal 

 rib (cf. Figure IX). Case B. English. Adult. Male. '/» Nat. size. See also Figure III. 



Illustrates type of cervical rib whose independent ossification proceeds only as 

 far the crossing of the sub-clavian artery. Groove for lowest brachial tiunk is 

 shown at N. This figure shows the variety of this type where an intermediary 

 cartilage exists between the two ribs. 



In such cases which have escaped complete inhibition of bony 

 tissue through nerve influence, a deep nerve groove is often present 

 on the cervical rib, but the shaft extends further forward in the root 

 of the neck. This nerve groove will be found in several of the 

 succeeding types. 



Another variety of cervical rib is shown in Fig. IV. 



This occurs twice on the left side and once on the right in the 

 present series from which the types were taken. The cervical element 



