180 OSTEOLOGY. 
Nutrient Foramina.—The foramina for the larger nutrient vessels, of which there may he 
one or two directed outwards, are usually found about the middle of the posterior border, or it 
may be opening into the floor of the groove for the subclavius muscle. 
‘Architecture.—The shaft consists of an outer layer of compact bone, thickest towards the 
centre, but gradually thinning towards the extremities, the investing envelope of which consists 
merely of a thin shell. Within the shaft the cancellous tissue displays a longitudinal striation, 
which internally assumes a more cellular appearance. At the acromial end the general arrange- 
ment of the fibres resembles the appearance of the sides of a Gothic arch. 
Variations.— The clavicles of women are more slender, less curved, and shorter than those of 
men. In the latter the bone is so inclined-that 1ts outer end hes slightly higher or on the same 
level with the sternal end. In women the bone usually slopes a little downward and outward. 
The more pronounced curves of some bones are associated with a more powerful development of 
the pectoral and deltoid muscles, a circumstance which also affords an explanation of /the difter- 
ences usually seen between the right and left bones, the habitual use of the right-upper Limb 
reacting on the form of the bone of that side. 
Ossification.—Phylogenetically of dermic origin, the claviele in man is remarkable in 
commencing to ossify before 
Sternal epiphysis ossifies about Primary centre appears about ‘ rs 
20th year; fuses about 25th year 5th or 6th month of foetal life any) other bone i ue the body ; 
this occurs as early as the 
fifth or sixth week of foetal 
life. The primitive centre 
from which the shaft and 
outerextremity aredeveloped 
appears prior to the forma- 
Frc. 124.—OssIrIcaTION OF THE CLAVICLE. tion of any cartilaginous 
matrix ; and it is not tilla 
later stage that cartilage plays a part in the development of the bone by assisting in the 
growth of its extremities. 
A secondary centre or epiphysis appears at the sternal end about the age of twenty 
or later, and fusion rapidly occurring between it and the shaft, ossification is completed 
at the age of twenty-five or thereabouts. 
THE SCAPULA 
The scapula (scapula), shoulder blade or blade bone, is of triangular shape and 
flattened form. It has two surfaces, ventral and dorsal. From the latter there 
springs a triangular process called the spine, which ends externally in the acromion ; 
whilst from its superior border there arises a beak -like projection called the 
coracoid process. 
The body of the bone, which is thin and translucent, except along its margins 
and where the spine springs from it, has three borders and three angles. Of these 
borders the internal or vertebral (margo vertebralis) is the longest ; it stretches 
from the superior angle above to the inferior angle below. Of curved or somewhat 
irregular outline, it affords a narrow surface for the insertion of the levator anguli 
scapule, rhomboideus minor, and rhomboideus major muscles. 
The superior border (margo superior), which is thin and sharp, is the shortest of 
the three. It runs from the superior angle towards the root of the coracoid process, 
before reaching which, however, it is interrupted by the suprascapular notch (in- 
cisura scapulie), which lies immediately to the inner side of the base of that process. 
This notch, which is converted into a foramen by a ligament, or occasionally by a 
spicule of bone, transmits the suprascapular nerve. Attached to the superior 
border, close to the notch, is the posterior belly of the omo-hyoid. The eaternal or 
axillary border (margo axillaris), so called from its relation to the hollow of the 
armpit (axilla), is much stouter than either of the others; it extends from the 
external angle above to the inferior angle below. The upper inch or so of this 
border, which lies immediately below the glenoid articular surface, is rough and 
tubercular (tuberositas infraglenoidalis), and affords attachment to the long head 
of the triceps. Below this there is usually a groove which marks the position of 
the dorsal artery of the scapula. The swpertor angle (angulus medialis) is sharp 
and more or less rectangular; the inferior angle (angulus inferior) is blunter and 
more acute; whilst the eaternal angle (angulus lateralis) corresponds to that part 
of the bone which is sometimes called the head, and which supports the glenoid 
surface and the coracoid prceoss. 
