SHOULDER GIRDLE. 77 



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entirely disappear long before birth. The hyoid, then, 

 with its cornua and ligaments answers pretty much to a 

 gill-arch, or really to parts of two gill-arches, since the 

 great and small cornua belong to originally separate arches 

 present at an early stage of development. It is a remnant 

 of a structure which has no longer any use in the Human 

 Body; but in the young frog-tadpole parts answering to 

 it carry gills and have clef ts between them which extend 

 into the throat just as in fishes. The gills are lost after- 

 wards and the clefts closed up when the frog gets its lungs 

 and begins to breathe by them. In the embryonic human 

 being these gill-clefts are also present and several more- 

 behind them, but the arches between them do not bear 

 gills, and the clefts themselves are closed long before birth. 

 As they have no use their presence is hard to account for; 

 those who accept the doctrine of Evolution regard them as 

 developmental reminiscences of an extremely remote ances- 

 tor in which they were of functional importance somewhat 

 as in the tadpole; of course this does not mean that men 

 were developed from tadpoles. 



The Appendicular Skeleton. This consists of the 

 shoulder girdle and the bones of the fore limbs, and the 

 pelvic girdle and the bones of the posterior limbs. The two- 

 supporting girdles in their natural position with reference 

 to the trunk skeleton arc represented in Fig. 29. 



The Shoulder Girdle, or Pectoral Arch. This is made 

 up on each side of the scapula or shoulder -Hade, and the 

 clavicle or collar-bone. 



The scapula (8, Fig. 29) is a flattish triangular bone 

 which can readily be felt on the back of the thorax. It is 

 not directly articulated to the axial skeleton, but lies im- 

 bedded in the muscles and other parts outside the ribs on 

 each side of the vertebral column. From its dorsal side- 

 arises a crest to which the outer end of the collar-bone is 

 fixed, and on its outer edge is a .shallow cup into which the 

 top of the arm-bone fits; this hollow is known as the glenoid 

 fossa. 



The collar-bone (0, Fig. 29) is cylindrical and attached 



