Chap, ix.] PECTORAL ARCH. 349 



Fishes, where there is no sternum, the coracoids early 

 unite in the ventral median line ; where a sternum is 

 present the coracoid of either side enters into con- 

 nection with it. In the hind arch, where there is no 

 bar corresponding to the sternum, the pubes and ischia 

 may unite with their fellows at a symphysis, as in all 

 Mammalia ; in all Vertebrates above fishes, the ilia 

 enter into a more or less firm union with the sacral 

 region of the axial skeleton, or vertebral column. 

 (See page 321.) 



Just as in the case of the skull, when covering 



/ o 



membrane bones are developed some enter into union 

 with the cartilage or cartilage bones of the pectoral 

 arch, but no such bones go to form part of the pelvis. 

 The most important of these bones is the clavicle, 

 with which in some fishes a supraclavicle, con- 

 nected with the skull, and an iiifraclavicle, united 

 with its fellow below, are added on ; in the Amniota 

 an iiiterclavide is sometimes developed. As we 

 ascend the scale we observe a reduction in the cora- 

 coidal region ; thus the precoracoid is absent in the 

 crocodiles, and among birds is found in a rudimentary 

 condition in the Ratitae only ; in mammals it is never 

 present, and the Prototheria alone have a fully de- 

 veloped coracoid ; as a rule the scapular end of the 

 bone is alone retained ; it is, indeed, from the hook- 

 like form of its remnant in man that the bone has 

 received its name. In a few (shrew, mouse) the 

 sternal end of the coracoid is persistent (Gegenbaur). 



In Chamseleons and Crocodiles the clavicle is lost, 

 as it is also in many Ratitse, where, if present, it is 

 only rudimentary ; in the Carinatse the two clavicles 

 unite to form a single bone, the furcula (" merry- 

 thought "), which becomes connected by ligaments 

 with and strengthens the cariiia steriii (Fig. 145). 

 Among mammals the clavicle may be well developed, 

 as in man and the bat, bony in its median region 



