108 



OSTEOLOGY. 



border, and in conjunction with the facet on the inferior edge of the manubrium 

 forms a recess on either side, in line with the articulation between the manubrium 

 and body, into which the cartilage of the second rib fits. The inferior border of the 

 body is curved, and is united in the middle line with the xiphoid process, 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 process. The middle line of the body 

 of the sternum anteriorly corresponds to the floor of the medial surface furrow, which 

 runs down the front of the chest in the interval between the two great pectoral 

 muscles. The posterior surface is slightly 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 inferior extremity, on each side, to a transversus thoracis muscle. 

 The xiphoid process displays many varieties of form and structure. It 

 is a pointed process of cartilage, supported by a core of bone connected above 

 with the inferior end of the body of the sternum, and having its lower extremity, 

 to which the linea alba is attached, free, tt lies somewhat posterior to the plane 

 of the anterior surface of the manubrium, and forms a floor to the V-shaped 

 interval between the cartilages 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 transversus thoracis muscles derive attachment from it. It remains partly 

 cartilaginous until middle life, at which time it generally undergoes ossification, 

 particularly at its upper part, becoming fused with the body. Of varied form, 

 it may be met with of spatula -shape, bifid, circular, pierced in the centre, or 

 twisted and deflected to one or other side, or turned forward. 



The sternum as a whole is broadest above, where the first rib cartilages are 

 attached. It becomes narrow opposite the second rib cartilages, but again expands 

 until the level of the fifth rib cartilage is reached, below which it is rapidly 



reduced in width and ends 

 below in the pointed xiphoid 

 process. Its position in the 

 body is oblique from above 

 downwards and forwards; its 

 axis, if prolonged upwards, 

 would touch the vertebral 

 column opposite the third 

 or fourth cervical vertebra. 

 Though liable to changes in 

 position by the rising and fall- 

 ing of the chest wall, its upper 

 extremity corresponds to the 

 level of the lower border of the 

 second thoracic vertebra, whilst 

 the lower end of the xiphoid 

 process usually falls in line 

 with the fibro - cartilage be- 

 tween the tenth and eleventh 

 thoracic vertebrae. 



At birth. 



At 3 years. 

 FIG. 122. OSSIFICATION OP THE STERNUM. 



In this figure the second as well as the third segment of the body 

 possesses two centres. 



1. Appears about 5th or 6th month. 2. Appear about 7th month ; 

 unite from 20 to 25. 3. Appear about 8th or 9th month ; third seg- 

 ment unites with second about puberty ; fourth segment unites with 

 third in early childhood. 4. Appears about 3rd year or later. 



In women the sternum as a whole 

 is usually narrower and shorter than 

 in men, and its position less oblique. 

 On the other hand, Paterson has 

 shown that the male manubrium is 

 proportionately wider and shorter 

 than the female, whilst the male body is proportionately longer and narrower than the female. 



Ossification. The cartilaginous sternum, developed from the fusion, in the median 

 plane, of two cartilaginous bands uniting the anterior extremities of the cartilages of the 

 first eight ribs, according to the researches of Ruge and more recently of Eggeling, begins 



