265 



IL Types in the descending scale. 



As a necessary preliminary to the study of these types attention 

 is drawn to tlie condition represented in Eig. YII. This I have pre- 

 viously termed the "rocker" variety of first rib. It will be seen that 

 the rib is twisted on itself and at the lowest part of the curve is a 

 deep well-defined groove bounded in front by scalenus anticus inser- 

 tion and behind by the attachment of scalenus medius. The vein 

 marking is very ill-defined. Although this specimen was only seen 

 after maceration, the oblique direction of the sulcus sub-claviae, its 

 single channel, the as- 

 sociated slight impres- 

 sion made by the vein 

 and the marked defor- 

 mation of shape (i. e. 

 the twist) all indicate 

 that the nerve was re- 

 sponsible for the sul- 

 cus sub-claviae in this 

 instance. 



Fig. VIII shows 

 a type of first rib 



where the venous holl- 

 owing is exceedingly 

 well marked while the 

 impressions of nerve 

 and artery, although 

 easily distinguished, 

 are comparatively 

 poorly developed. 



As in the case of 

 the seventh cervical 

 rib so in this the nerve 

 and the vein exert as 

 potent an influence on 

 the appearance of the 



Fig. VII. Fig. VIII. 



Fig. VII. First dorsal rib right side. Case 2/807. 

 Nubian series. Vs Nat. size. 



Shows appearance of upper surface of Rocker rib 

 (see (I). A very well marked groove is present and has 

 been caused by the passage of the lowest brachial nerve 

 trunk (N). The vein marking (V) is less distinct but 

 is visible. The arterial impression does not occur on 

 this specimen. The rib illustrates the power of nerve 

 influence in modification of bony appearances. 



Fig. VIII. First dorsal rib left side. Adult. Male. 

 Case 89/7. Nubian series. '/^ Nat. size. 



To illustrate the modifying influence of the sub- 

 clavian vein on the appearance of the first rib. In this 

 specimen grooves for nerve artery and vein are all 

 shown at the inner border. The venous impression makes 

 a distinct hollowing of the upper surface of the bone. 

 The grooves for nerve and artery both become confluent 

 with this saucerlike depression caused by the reservoir 

 type of sub-clavian vein mentioned in the text. 



rib as does the artery. 



Fig. IX illustrates a type of first dorsal rib which is fused with 

 the second dorsal at the point where the artery passes outwards. It 

 presents but poorly marked impressions for the artery and the nerve. 



