92 OSTEOLOGY. 
The body (corpus sterni), usually twice the length and from half to two-thirds 
the width of the manubrium, displays evidence of its composite nature. If the 
anterior surface, which is slightly convex from above downwards, and faintly 
concave from side to side, be carefully examined, three ill-marked ridges may be 
seen crossing it transversely; these correspond to the lines of fusion between the 
four primitive segments. To this surface of the bone the great pectoral muscles 
are extensively attached on either side of the middle line. The lateral borders are 
thick and interrupted at points corre- 
sponding to the transverse lines already 
mentioned by U-shaped hollows, the 
edges of which are more or less project- 
ing. These are for the reception of the 
¢ cartilages of the third, fourth, and fifth 
ribs. The wpper border is united to the 
manubrium above, and forms with it an 
angle of variable degree—the sternal 
angle (angulus sterni). A small facet is 
formed at the expense of the outer ex- 
tremity of this border, and in conjune- 
tion with the facet on the lower border 
of the manubrium forms a recess on 
either side, in line with the angle, into 
which the cartilage of the second rib fits. 
Pectoralis The lower border of the body is curved, 
major and in the middle line is united with 
the xiphoid cartilage, whilst on either 
side it is pitted to receive the cartilages 
of the sixth and seventh ribs, the latter 
being in part supported by the xiphoid 
cartilage. The middle line of the body 
of the sternum anteriorly corresponds 
to the floor of the median surface furrow, 
which runs down the front of the chest 
in the interval between the two great 
pectorals. The posterior surface 1s 
shghtly concave from above downwards, 
and displays faint indications of three 
transverse lines in correspondence with 
those placed anteriorly. It is in relation 
with the pleura and pericardium, and 
affords attachment at its lower extremity 
to the triangularis sterni muscle. 
The xiphi-sternum (processus xiph- 
Rectus oideus) displays many varieties of form 
abdominis and structure. It is a pointed ‘process, 
of cartilage, supported by a core of bone 
connected above with the lower end of 
the body of the sternum, and having its 
: lower extremity, to which the linea alba 
Fic. 70.—THE STERNUM (anterior view). is attached, free. It lies somewhat pos- 
terior to the plane of the anterior surface 
of the manubrium, and forms a floor to the V-shaped interval between the carti- 
lages of the seventh ribs. In this way a depression is formed, the surface hollow 
in correspondence with which is called the pit of the stomach or infrasternal 
depression. To the sides of this process are attached the aponeuroses of the 
abdominal muscles, whilst posteriorly the fibres of the diaphragm and triangularis 
sterni muscles derive attachment from it. It remains partly cartilaginous until 
middle life, at which time it generally undergoes ossification, particularly at its 
upper part, and becomes fused with the body. Of varied form, it may be met 
Interclavicular notch Sterno-mastoid 
Clavicular facet 
car- 
II. Rib cartilage 
III. Rib cartilage 
Body 
IV. Rib cartilage 
V. Rib cartilage 
VI. Rib cartilage 
VII. Rib eartilage. 
Ensiform process 
