50 Anatomy of Skeleton 



body. By pushing the fingers up in the axilla the third rib can be reached. The 

 second rib can only be found in front, where its cartilage is very apparent. 



Now look at the thorax from behind. The large flat muscles only cover the outer 

 aspect of the ribs, and the surface pertaining to them only extends to the line of the 

 angles of the bones : internal to this line the ribs are covered by the muscles of the 

 Erector spins group, and even outside the line the upper and lower ribs are covered 

 by the Serrati postici passing to their attachments on them. The line of the angles 

 is not vertical : it is furthest from the middle line usually on the eighth rib, and turns 

 in above and below this, so that it practically coincides with the tubercle on the first 

 rib and thus brings the outer border of the muscle group up to their insertions on the 

 cervical transverse processes. In the same way, below the eighth rib, the width of 

 the muscle mass decreases toward that of the back of the sacrum. 



Now observe the change in the relations of the ribs that results from movement of 

 the scapula. That bone covers the second to the seventh rib, but is separated from 



* Vl^f.f: .1 't -*^A ~ 111 



f\ 



FIG. 41. Upper surface of left first rib. A. head ; B. neck ; CC. calcified costal cartilage : 

 ; iti Serr. origin of Serratus magnus from outer border ; N. groove made by first dorsal 

 nerve. 



them by Subscapularis and Serratus magnus. When the shoulders are " brought 

 together " the vertebral margin of the scapula and its attached structures may ride 

 over the post- vertebral fascia, so that Serratus magnus covers the bones as far as the 

 angle. fBut when the angle of the scapula is brought outwards and the whole bone 

 rotated, as in raising the arm above the shoulder, the Serratus magnus and vertebral 

 border come away from the angles, and the Rhomboid muscles get into relation with 

 that portion of the bones that was formerly covered by Serratus magnus external to 

 the angles of the ribs : this can be appreciated by rotating the scapula on its clavicular 

 attachments in the skeleton. Owing to the presence of the scapula, the upper ribs 

 cannot be directly examined from behind. Below the seventh, however, the ribs can be 

 felt, though the twelfth is often impalpable in women. 



A brief examination shows that the upper and lower members of the series differ 

 decidedly from the majority of ribs : the chief points of distinction are as follows : 



First Rib. Articulates with one vertebra. Short, flat, and comparatively broad, 

 presenting upper and lower surfaces with inner and outer margins, instead of the 



