OSTEOLOGY. 
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(oP) 
The anterior or sternal extremity of the shaft, often slightly enlarged, displays 
an elongated oval pit into which the costal cartilage is sunk. 
Peculiar Ribs.—The first, second, tenth, eleventh, and twelfth ribs all display 
characters by which they can be readily recognised. 
The first rib can be easily distinguished from the others by its size, curvature, 
and flattened form. The head, which is of small size, has a single oval or circular 
facet, which is directed inwards and slightly backwards for articulation with the 
side of the body of the first dorsal vertebra. The neck is flattened from above 
downwards, and is shghtly down-turned towards the end which supports the head. 
Its anterior border is rounded and smooth ; its posterior edge rough for the attach- 
ment of ligaments. At the point where the neck joins the shaft posteriorly, a 
prominent tubercle curves upwards and backwards. The inner and under surface 
of this process has a small circular facet which rests on a corresponding articular 
surface on the transverse process of the 
first dorsal vertebra. The angle coin- 
cides with the tubercle, and thus assists 
in emphasising its prominence. The 
surfaces of the body of the rib are 
directed upwards and downwards, its 
borders inwards and outwards. If the 
finger be run along the thin inner 
border, a distinct spine or tubercle can 
Surface for attachment be readily felt about an inch or an inch 
-—— ofscalenusmedius and @ quarter {rom its amlenersers 
Groove for sub- 
Van rteny tremity. This is the scalene tubercle 
Sealenus posticus 
(tuberculum scaleni)for the attachment 
of the scalenus anticus muscle. There 
Sealenus anticus ig a shallow, oblique groove crossing 
aes the upper surface of the shaft in front 
of this for the lodgment of the sub- 
elavian vein; whilst behind the 
tubercle there is another groove, 
usually better marked, and passing 
{ suv. obliquely forwards for the subclavian 
cavins artery (sulcus subclavie). The space 
on the upper surface of the rib between 
this latter groove and the tubercle 
posteriorly is somewhat rough, and 
affords attachment to the fibres of the 
scalenus medius muscle. The anterior 
i extremity of the rib is thickened and 
Fie. 74,—-Frrst AND) SECOND PGES Rips aS SEEN often expanded for the reception of 
ee its costal cartilage, which is not 
infrequently ossified. The under surface of the rib is smooth and is covered | vy 
pleura. The outer convex border, thin in front, is usually thick and rough behind 
the subclavian groove, where it has attached to it the fibres of the first digitation 
of the serratus magnus. Along this edge, also, are attached the external and 
internal intercostal muscles of the first. intercostal space. The inner concave 
border is thin, and has connected with it the aponeurotic expansion kndwn as 
Sibson’s fascia. 
The second rib may be distinguished by the size of its curve; the absence of 
any twist on its shaft, so that it can be laid flat on the table; the oblique direction 
of the surfaces of its shaft, the outer being directed upwards and outwards, whilst 
the inner is turned downwards and inwards; and the presence of a well-marked, 
rough, oval area about the middle of its outer surface and lower border for part 
of the first, and the whole of the second digitation of the serratus magnus muscle. 
The head has two facets, and the angle is close to the tubercle posteriorly. 
The tenth rib has usually only a single articular facet on the head. 
The eleventh and twelfth ribs are recognised by their length. Their heads, 
Scalene tubercle 
Serratus magnus 
