184 OSTEOLOGY. 
fore part ef the coracoid appears in the first year, and fusion along an oblique line leading 
from the upper edge of the glenoid fossa to the conoid tubercle is complete about the 
fifteenth year. A separate centre (subcoracoid), which ultimately includes the upper part 
Appears about of the glenoid fossa and 
16-17 yrs.; fuses external part of the 
Acromial centres about 20 yrs. Ein seks $2 b ye : : 
appears 15-16 yrs. ; Subcoracoid centre coracoid process, makes 
fuses about 25 zr. g _appears 10 yrs.; fuses its appearance about the 
- 16-17 yrs. : / 
Secondary centre for WW Appears about tenth year, and fuses 
Primary centre coracoid appears i _—17 yrs.; fuses with the surrounding 
appears about about end Ist yr.; = ET about 20 yrs. 4 ies . 
2nd m. foetal life. fuses about 18 yrs. <2 bone about sixteen or 
seventeen. Up till the 
age of puberty the acro- 
mion remains cartilagin- 
ous ; centres, two or more 
in number, then make 
their appearance, which 
coalesce and ultimately 
unite with the spine 
about the twenty - fifth 
vear. Failure of union 
may, however, persist 
/ sears sir throughout life (see ante, 
// yrs.; fuses20- Variations). 
foes Ossification commences 
in the cartilage in the 
inferior angle about 
AY 
LIN 
Appears about 
16 or 17 yrs. ; 
fuses 18-20 yrs. 
Appears 16-17 yrs. ; 
fuses 20-25 yrs. puberty, and  indepen- 
Scapula at end of First Year. Scapula about the Age of Puberty. dently and a little 
Fic. 127. —OsstrIcaTION OF THE SCAPULA. later, along the verte- 
bral margin, fusion 
with the body occurring at from twenty to twenty-five years. 
Small scale-like epiphyses make their appearance on the upper surface and at the 
extremity of the coracoid, and are completed about the twentieth year. A thin epiphysial 
plate develops over the lower part of the glenoid fossa about sixteen or seventeen, fusion 
being complete about eighteen or twenty vears of age. 
THE HUMERUS. 
The humerus, or bone of the upper arm, articulates with the scapula above and 
with the bones of the forearm, the radius and ulna, below. Its upper end com- 
prises the head and great and small tuberosities ; its shaft, which is longer than any 
of the other bones of the upper extremity, is cylindrical above and flattened below, 
where it ends in the inferior extremity, which is expanded to form the condyles on 
either side, and supports the trochlear and capitellar articular surfaces for the ulna 
and radius respectively. ; 
The superior extremity is the thickest and stoutest part of the bone. The head 
(caput humeri), which forms about one-third of a spheroid and is covered by 
articular cartilage, is directed upwards, inwards, and slightly backwards, and rests in 
the glenoid fossa of the scapula; the convexity of its surface is most pronounced in 
its posterior half. Separating the head from the tuberosities externally is a shallow 
groove, Which fades away on the surface of the bone which supports the articular 
surface inferiorly. This is named the anatomical neck (collum anatomicum) and 
serves for the attachment of the capsule of the shoulder joint. The articular edge of 
the groove opposite the small tuberosity is usually notched for the attachment of the 
superior gleno-humeral hgament. The great tuberosity (tuberculum majus) abuts 
on the outer side of the head and becomes continuous with the shaft below. Its 
upper surface forms a quadrant, which is subdivided into three more or less smooth 
areas of unequal size. Of these the highest and anterior is for the insertion of the 
supraspinatus muscle, the middle for the infraspinatus, whilst the lowest and 
posterior serves for the insertion of the teres minor muscle. The outer surface of 
this tuberosity, which bulges beyond the line of the shaft, is rough and pierced by 
numerous foramina, Anteriorly the great tuberosity is separated from the small 
