102 



THE SKELETON 



The tenth rib lias usually a single facet on its head. Occasionally a second is 

 }»resent. When this is the case, the ninth thoracic vertebra is not exceptional, and 

 presents two (U-nn-facets. 



The eleventh rib has a single facet on the head. The angle is feebly marked, 

 and the subcostal groove shallow. It lacks a neck and tubercle. 



The twelfth rib has a large head furnished with one facet. The shaft is 

 narrow, and its length extremelv variable. It may be as short as 3 cm. , or attain 

 a length of 20 cm. (8"). 



Tlie twelfth rib eives attachment to the following muscles: — 



Internal intercostal. 

 External intercostal. 

 Levator costfe. 

 Diaphragm. 



Transversalis abdominis. 

 External oblique. 



Internal oblique. 

 Serratus posticus inferior. 

 Musculus accessorius. 

 Sacro-lumbalis or ilio-costalis. 

 Erector spinae. 

 Quadratus lumborum. 

 Latissimus dorsi. 



Fig. 111. — Rib at Puberty. 



EPIPHYSIS FOR THE HEAD. APPEARS AT 

 FIFTEEN ; FUSES AT TWENTY-THREE 



EPIPHYSIS FOR TUBERCLE. APPEARS AT 

 FIFTEEN; FUSES AT TWENTY-THREE 



THE CARTILAGINOUS SHAFT COMMENCES TO OSSIFY 

 AT THE EIGHTH WEEK OF INTRA-UTERINE LIFE 



Tiic costal cartilages are bars of hyalin<' cartilage attached to the anterior 

 extremities of the ribs; they represent unossified epiphyses. Like the shaft of 

 a ril), each has an outer and inner surface; the outer surfaces give origin and 

 insertion to large muscles; and the inner surfaces, from the second to the seventh 

 inclusive, are in relation with the triangularw sterni. The upper and lower borders 

 serve for the attachment of the internal intercostal muscles. The upper seven 

 cartilages, and occasionally the eighth, are connected with the sternum. The first 

 fuses with the manubrium; the remaining six are received in small articular con- 

 cavities, and retained by means of Hgaments. The cartilages of the vertebro-chondi-al 



