106 



THE BONES OF THE UPPER LIMB. 



OSSIFICATION OF THE BONES OF THE UPPER LIMB. 



With the exception of the clavicle, all the bones of the upper limb begin to ossify in 

 cartilage 



The clavicle begins to ossify before any other bone in the body. Its ossification com- 

 mences before the deposition of cartilage in connection with it, but afterwards progresses in 

 cartilage at both ends, as well as in fibrous substance. It is formed from one principal 



Fig. 115. OSSIFICATION OF THE CLAVICLE. (R. Quain.) 



a, the clavicle of a foetus at birth, osseous in the shaft, 1, 

 and cartilaginous at both ends. 



b, clavicle of a man of about twenty-three years of age ; 

 the shaft, 1, fully ossified at the acromial end; the sternal 

 epiihysis, 2, is represented rather thicker than natural. 



centre, appearing about the 6th week, to which is added an epiphysis at the sternal end. 

 The epiphysis appears from the 18th to the 20th year, and is united to the shaft about the 

 25th year. 



The scapula is ossified in two principal pieces, one forming the body or scapula proper, and 

 the other the coracoid process, which is generally regarded as representing the independent 



1 year. 15 cr 16 years. 17 or 18 years 22 years. 



Fig. 116. OSSIFICATION OF THE SCAPULA. (R. Quain.) 



1, scapula proper, including the body and spine ; 2, coracoid ossification; 3, 5, nuclei of acromion ; 

 4, epiphysis at the lower angle ; 6, epiphysis on vertebral border. 



In A, ossification has commenced in the coracoid process. In B the coracoid process (represented as 

 too little ossified in the figure) is now partially united at its base, and centres have appeared in the 

 acromion and at the lower angle. In C, a second point has appeared in the acromion, and a long 

 epiphysis on the vertebral border. In D, the acromion, and the epiphysis of the vertebral border are 

 still separate. 



and often largely developed coracoid bone of the monotremata and lower vertebrates. The 

 centre of the body appears near the head, about the 7th or 8th week, and gives rise to a 

 triangular plate of bone, towards the upper margin of which, about the 3rd month, the spine 

 appears as a slight ridge. At birth, the coracoid and acromion processes, the base and inferior 

 angle, the edges of the spine and of the glenoid cavity are cartilaginous. The greater part of 

 the coracoid process is formed from a centre which appears in the first year, but a small part 

 at the base of the process, including the upper extremity of the glenoid cavity, is a separate 

 ossification (subcoracoid), commencing about the tenth year. 1 The coracoid process joins the 

 body about the age of puberty, and at this time epiphyses make their appearance. In the 

 acromion two, sometimes three, nuclei appear between the 14th and 16th years; they soon 

 coalesce, and the resulting epiphysis is united to the spine from the 22nd to the 25th year. 

 The cartilage of the base, which it may be noticed corresponds to a more largely developed 



1 It is believed by some anatomists that the subcoracoid ossification is the true coracoid element of 

 the shoulder-girdle, and that the coracoid process represents the precoracoid of reptiles (Sabatier) or the 

 epicoracoid of monotremes (Howes). . 



