58 Anatomy of Skeleton 



The bone is broadest across the manubrium, and then opposite the junction of 

 the fifth cartilages with it. It is narrow at the angle and still more so at the junction 

 with the xiphoid. 



The top border of the manubrium presents a central notch, the suprasternal, inter- 

 clavicular, or jugular notch ; outside this is an articular facet for the clavicle on the upper 

 lateral angle of the bone : the facet is concave from within out, slightly convex from 

 before backward, and looks upwards and outwards and slightly backwards. The first 

 rib cartilage reaches the bone, just below this facet, on the upper part of the side 

 margin, and the second cartilage is connected with it opposite the angle, partly attached 

 to the manubrium and partly to the first segment of the body. Thus the manubrium 

 has one and a half cartilages connected with it on each side. On the body the third, 

 fourth, and fifth cartilages are attached respectively opposite the lines between the 

 segments as in the figure (Fig. 47), the sixth on the side of the last segment, and the 

 seventh partly on this and partly on the xiphoid. In the figure the eighth cartilage on 

 one side also reaches the xiphoid, an occurrence occasionally met with. 



Thus each sternebra bears two half facets on each side for the cartilages : in the 

 case of the second cartilage the articular cavity on the sternebra is separated from that 

 on the manubrium by an interarticular ligament attached to the cartilage in the angle, 

 making a double chondro-sternal articulation, and a corresponding condition may 

 obtain in the third and fourth joints, but frequently in these, and usually in the 

 remainder, the interarticular ligament is increased so that it obliterates one or both 

 of the small cavities. 



It may be noticed in this connection that there is usually some asymmetry of the 

 bone, most apparent in the levels of its lateral articulations. 



The manubrium, on its front surface, shows two ill-defined lateral hollows below 

 the clavicular level, from which the Pectoralis major muscles arise. The vertical 

 slightly raised area between these hollows forms a T-shaped ridge with a transverse 

 thickening that extends between the clavicular facets. Examination of the back of 

 the bone shows a corresponding transverse elevation, and thus the thickest part of the 

 manubrium, and indeed of the whole bone, is situated between the inner ends of the 

 clavicles, evidently to withstand the pressure of these bones and shocks transmitted 

 through them. 



On the front ridge, running down and in from the facet, is a rough area on each 

 side for the attachment of the sternal tendon of the Sterno-mastoid. Above and 

 between these the bone is hollowed, covered by subcutaneous tissues and forming the 

 floor of the supra-sternal hollow, and on the top margin is a roughness for the 

 attachment of the interclavicular ligament. 



The Pectoralis major meets its fellow in the middle line a variable distance above 

 the angle ; its area of origin then takes the front surface of the mesosternum to the 

 middle line, as far as the level of the fifth cartilages, where the area narrows towards 

 the sixth cartilage : this narrowing may commence one segment higher. All this 

 origin of the muscle is by fleshy fibres, so that no corresponding rough marking occurs 

 on the bone ; but the bare surface on the bone seen in the drawing below the areas 

 for the muscles is really covered by a thick layer of interlacing tendinous fibres directly 

 continuous with the Pectorals (see also Fig. 39) , and these fibres, decussating in the centre, 

 stream down over the end of the bone on to the surface of the xiphoid, where they are 

 blended with the aponeurotic abdominal layers of the linea alba : these aponeuroses are 

 the sheath of the Rectus, and some fibres of this muscle also reach the xiphoid. 



Probably these fibrous portions of the pectoral masses account for faint markings that mav 

 often be felt on the last segment of the body, frequently suggesting to the touch that there is another 



