44 THE HUMAN STERNUM 



This statement does not coincide with that of Birmingham,^ who states 

 that among thirty sterna examined by him, twelve were symmetrical in this 

 particular ; while in the remaining eighteen, ten showed an obliquity down- 

 wards and to the right ; eight showed an obliquity downwards and to the left. 



2. Lateral Curvature of the Sternum (T^hle^XN). In 35-6 per cent, of 

 the sterna examined, the long axis of the sternum presents a convexity 

 slight or well marked to the right or left. The convexity is more often to 

 the right (23*2 per cent.) than to the left (12-3 per cent.), and the curvature 

 occurs more often in adult (38*9 per cent.) than in young sterna (32'3 per 

 cent.) 



This agrees with Birmingham's conclusion. He found out of forty- 

 six cases examined, a curvature to the right in fifteen examples (3 2* 6 per 

 cent.), a curvature to the left in twelve cases (26'0 per cent.) 



3. Asymmetry in Attachment of the Costal Cartilages (Tables XVJI-XIX), 

 The young sternum is naturally straight and symmetrical. The alteration 

 in costal attachments appear to be caused by (i) alterations in the form 

 of the thorax brought about by movements, curvature of the spine, and 

 conditions affecting the viscera, (ii) obliquity in the osseous union of 

 the sternal elements, (iii) differences in the depth of the first pair of costal 

 cartilages, and (iv) alterations in the relative position of the sixth, seventh, 

 and eighth costal cartilages. 



Some degree of costal asymmetry is common, and is found in the 

 majority of adult sterna. 



It is more frequent in the adult {f><)'^ per cent.) than in the young 

 sternum (41 '2 per cent.) It is rather more common to find downward 

 displacement of the costal attachments on the left (57"4 per cent.) than on 

 the right side (42-5 per cent.) ; and in some cases there is asymmetry of 

 the costal cartilages in two directions in the same sternum. The cartilages 

 in or near the middle of the series are most frequently asymmetrical 

 in position ; and most rarely the seventh and first. The following is the 

 order of frequency : — 



Adult: 3rd, 2nd, 4th, 5th, 6th, 7th, ist. 

 Young : 4th, 5th, 3rd, 6th, 2nd, 7th, ist. 



