68 Anatomy of Skeleton 



The extent of the muscle insertion is constant, and does not necessarily correspond 

 with the length of the groove : the floor of the groove may present a ridge for an 

 intramuscular tendon. 



The Pectoralis major and Sterno-mastoid take origin from the clavicle by mixed 

 tendinous and muscular fibres, so that their area can be found and followed with the 

 eye and finger on any full-grown bone. The two areas are visible on the front (Fig. 54) 

 aspect of the bone, where the lower pectoral surface is seen to extend further out than 

 the upper one for the Sterno-mastoid : the latter surface is on the upper and front 

 and the pectoral area on the front and lower aspect of the inner part of the shaft. 

 Turn the bone up and follow the pectoral surface on its lower aspect, and it will be 

 seen (Fig. 53) that it extends back to come into relation with the rhomboid ligament 

 and costo-coracoid membrane. 



The attachments of Trapezius behind and Deltoid in front are plainly visible on 

 the outer third of the bone. A little interval exists between the Pectoral and Deltoid 

 origins, and here a communication between the cephalic vein and the external jugular 

 may cross the bone and may groove it : this is the persistence of a large venous 

 channel that is present in this situation in the embryo. 



The vaginal layer of deep cervical fascia, which encloses the Sterno-mastoid and 

 Trapezius, is attached to the bone along a line joining the areas for these two muscles : 

 there is no definite marking for it on the bone. In front of this line the clavicle is 

 covered only by Platysma and superficial tissues, and crossed under this by the 

 descending cervical nerves : some of these nerve filaments may groove the bone or 

 even pierce it, and their relation to the bone accounts for the excessive pain and tender- 

 ness that sometimes accompany and follow slight lesions of the bone. 



The inner curve in the clavicle arches over and protects the axillary sheath. 

 The relation of the sheath to the bone is shown in Fig. 51 : it lies behind and below 

 it and not quite in contact with it. The omohyoid fascia comes down into the 

 groove between the back of the bone and the sheath and obtains attachment to this 

 aspect of the bone, low down on its posterior surface : the line of its attachment lies 

 between the conoid and rhomboid impressions, and the double-layered fascia passes 

 externally on to the conoid ligament and so reaches the base of the coracoid process of 

 the scapula and the suprascapular ligament. Internally, the two layers separate at 

 the rhomboid impression, the deeper one passing down the rhomboid ligament to reach 

 the cartilage of the first rib below the origin of Sterno-thyroid, while the superficial 

 layer runs inwards along the back of the clavicle above the origin of Sterno-hyoid to 

 reach the top and back of the manubrium. In this way the central infrahyoid muscles 

 are included between the layers as well as the (lateral) omohyoid, so that all the muscles 

 of this group are in one sheet or morphological plane. 



The suprascapular artery runs out behind the bone, held to it by the omohyoid 

 fascia, and it gives off here the small nutrient artery which pierces the bone behind 

 and below, running in an outward direction : the foramen may not always be present 

 or it may be double. It is worth remarking that there is always an artery running 

 behind the bone and derived from the thyroid axis, but it does not always reach the 

 scapula : in this case the effective suprascapular artery arises from the third part of 

 the subclavian artery, runs out more or less in company with the nerve, and passes 

 with it under the suprascapular ligament. 



The morphological value of the clavicle is uncertain. It has been customary to 

 look on it as a bone that has been secondarily added to the pectoral arch, of which it 

 is not really a constituent, in the sense that it does not represent one of the ventral 

 segments of that arch already shortly described. 



