PRACTICAL CONSIDERATIONS : THE SCAPULA. 



253 



the lower angle is sharp, the process on the front border small ; the hind border 

 straight up to the spine, then slanting forward in another straight line ; the upper 

 border descends sharply ; the coracoid is slight, with the end compressed instead of 

 knobbed ; the acromion is curved and narrow. An expert should be reasonably 

 sure of the sex four times in five. Doubtful bones are almost always male ; so are 

 those of peculiar shape, with the exception of concave vertebral borders. The 

 scapular index has no sexual significance.^ 



Structure. — The strong parts are seen when the bone is held to the light. 

 The head, neck, coracoid, acromion, and most of the spine are strong. So also 

 are the front border, the lower angle, and, to a less extent, the hind border, which 

 is strongest above the spine. Most of the body is very thin. A section through 

 the socket, along the origin of the spine, shows the bony plates so disposed as to 

 resist pressure in that line. 



Development. — There is one chief centre for the scapula proper and one for 

 the coracoid, besides an indefinite number of accessory ones. The first appears 

 about the eighth week (Rambaud et Renault) at the neck, and forms nearly the 



Fig. 272. 



Ossification of scapula. A, at eighth foetal month ; B, towards end of first year ; C, from fourteen to fifteen years ; 

 £>, from seventeen to eighteen years; E, about twenty years, a, chief centre; l>, for coradoid process; c, for acro- 

 mion ; d, for inferior angle ; e, additional for acromion ; /', for vertebral border. 



whole bone, including the spine and the root of the acromion and the dorsal part of 

 the root of the coracoid. The coracoid centre appears in the first year ; it forms 

 also the top of the glenoid cavity, and fuses with the first at fourteen or fifteen, 

 beginning to unite at the ventral surface. At the earlier age the acromion is carti- 

 lage beyond a line drawn from the back of the clavicular facet to the front of the 

 metacromion. At about fifteen many little nuclei appear in the acromion. The 

 anterior tubercle is formed from a single nucleus ; the others coalesce into two 

 groups, — one in the centre, the other at the outer margin. At about eighteen the 

 latter joins the body and the other two fuse. A year later the mass so formed also 

 joins the body. Sometimes this remains connected by fibro-cartilage ; very rarely 

 several pieces persist. A scale-like epiphysis appears at the conoid tubercle of the 

 coracoid about fifteen, and soon fuses. About seventeen or eighteen a nucleus 

 appears in the strip of cartilage along the posterior border and one at the lower 

 angle. Both are generally fused by twenty, but the lower is one of the last to fuse 

 in the skeleton, and the line of union may remain for years. 



PRACTICAL CONSIDERATIONS. 



The scapula is rarely absent and rarely malformed. The outer part of the 

 acromion may exist as a distinct bone, as may, but less frequently, the coracoid. 

 Many cases of so-called fracture of the acromion and others of supposed traumatic 

 separation of the acromial epiphysis are probably cases of persistent epiphysis. The 

 centre for the inferior angle sometimes remains distinct, being united to the body 



' Dwight : The Range and Significance of Variation in the Human Skeleton, Proc. Mass. 

 Med. Soc, 1894. 



