74 



Anatomy of Skeleton 



which plays against its deep surface. In some animals, as in the rabbit, the angle is 

 drawn out into a long " metacromial " process. 



Observe that the facet for the clavicle occupies the greater part of the inner border 

 of acromion, so that Trapezius only reaches a very little part of this border before pass- 

 ing on to the clavicle, whereas the Deltoid arises along the whole of the outer border 

 and then along the front before it reaches the clavicle. Also observe that both muscles 

 have comparatively broad markings for their attachments, which are evidently by 

 mixed muscle and tendon, and moreover the Deltoid area along the outer border has 

 four ridges on it which indicate the places of attachment of the intramuscular tendons 

 in this muscle (Figs. 57 and 59). 



The facet is obliquely cut, facing upwards and inwards, so that the clavicle is 



Concoid . 



FIG. 58. Dorsal surface of scapula in the sixth week." From a model. 

 There is no suprascapular notch because there is no supraspinous 

 fossa. The cartilaginous acromio-spinous bar is distinct ; the 

 interrupted line at its end indicates that it is lost in a condensation 

 mass which will chondrify later to form the acromion. The glenoid 

 cavity is partly on the coracoid. Note the small size of the areas 

 for Infraspinatus and Supraspinatus. 



placed on a slightly higher level and tends to ride over the acromion : this explains 

 the difficulty in retaining the bone in position when dislocation has occurred between 

 them. The rough area outside the facet is for ligaments which are strengthened by 

 fibres from Trapezius and Deltoid, thus being made stronger than the ligaments on the 

 inferior aspect. 



The remaining upper surface of the process is subcutaneous, and has ramifying 

 on it the small arteries of the " acromial rete." Its lower surface is smooth and is 

 lined in part by the subacromial bursa which separates it from the tendon of Supra- 

 spinatus (Figs. 51 and 57, 5) : near the tip, in front, this surface has a slightly marked 

 roughness for the attachment of the coraco-acromial ligament. The tendon and 

 bursa separate it from the capsule of the joint, over which it is slightly arched from 

 before backwards. 



The acromion is an epiphysis formed by centres occurring in the condensation in 



