i84 A MANUAL OF ANATOMY 



the acromion process, which may be connected with the spine by a plate of 

 cartilage, or by fibrous tissue. {4) Imperfect ankylosis of the coracoid process, 

 which, however, is extremely rare. 



Ossification. — ^The scapula has one primary centre and eleven secondary 

 centres. The primary centre appears in the body near the neck about the 

 8th week. 



The coracoid process, cartilaginous at birth, has four secondary centres — 

 coracoid, accessory coracoid, supracoracoid, and apical. The coracoid centre 

 appears in the end of the 15^ year, and gives rise to the chief part of the process, 

 which joins about the i sth year. The accessory coracoid centre appears about 

 puberty, and soon joins the main coracoid. It forms the triangular part of 

 the process which enters slightly into the extreme upper and inner part of the 

 glenoid cavity. The supracoracoid centre appears about the iSth year, and 

 forms a thin laminar epiphysis on the upper surface of the process. It gives 

 about the 25^/1 year. The apical centre appears about the i^tth year, and 

 forms an epiphysis which caps the tip of the process, and joins about the 

 2$th year. 



Acromion Process. — The inner or basal portion is ossified from the spine, 

 which in turn is ossified from the primary centre for the body. The greater 

 portion constitutes an epiphysis, which has two secondary centres. These 

 appear about the i6th year and soon join. The acromial epiphysis usually 

 joins the rest of the process about the 25^^ year or earlier. Union, however, 

 may not take place, and then the acromial epiphysis forms a separate acromial 

 bone, connected with the rest of the process by cartilage or by fibrous tissue, 

 and this condition may simulate a fracture. 



Glenoid Cavity. — The fundus or bed of this cavity is ossified from tlie 

 primary centre for the body, and its extreme upper and inner part is formed 

 from the accessory coracoid centre. Besides these the cavity has two special 

 secondary centres — supsrior and inferior. The superior glenoid or sub- 

 coracoid centre appears about the loth year, and it joins the fundus or bed 

 of the fossa about the i6th year. The inferior glenoid centre appears about 

 the i6th year, and forms' the glenoid epiphysial plate. It joins about the 

 20th year, and gives rise to the slight concavity of the fossa. 



The other secondary centres are allocated as follows: (i) Posterior border 

 of spine; (2) inferior angle; (3) base. These centres appear about the \bth 

 year, and join about the 25th year. 



The Humerus. 



The humerus extends from the shoulder to the elbow, its direction 

 being downwards and slightly inwards. It is a long bone, and is 

 divisible into a shaft and two extremities, upper and lower. 



The upper extremity includes the head, anatomical neck, great and 

 small tuberosities, commencement of the bicipital groove, and 

 surgical neck. The head, which is almost hemispherical, is smooth, 

 convex, and covered by cartilage. Its direction is upwards, 

 inwards, and backwards, and it articulates with the glenoid cavity 

 of the scapula. The anatomical neck is the constriction immedi- 

 ately beyond the cartilage of the head. It is best marked above, 

 especially between the head and great tuberosity, and it gives 

 attachment to the capsular ligament of the shoulder -joint. It is 



