24 



NATURAL HISTORY OF VERTEBRATES. 



Fig. 30. — Pertiiral girdle of embryo bird ; 

 cl, clavicle ; cr, coracoid; g/, glenoid fussa; 

 s, steinal ribs; j>c, scapula; s(, steruum ; r, 

 vertebral ribs. 



forming the so-called furcula, ' wish-bone,' or ' merry-thought.' This is generally 

 bound to the crest of the sternum, a part of the bone wiiich is largely episternal in 



its nature. In mammals, on the other hand, the 

 coracoid is, e.xcept in the monotremes, merely a 

 hook-like process of the scapula; the latter usually 

 develops a ridge or 'spine' for muscular attach- 

 ment, terminating in an acromion jirocess, to which 

 the dorsal end of the clavicle is attached, while 

 the ventral end of each clavicle is attached to the 

 sternum by means of the intervention of more or 

 less important remnants of the ejiisternnm (Fig. 

 15). Near these, remnants of the epicoracoid also 

 persist, especially in the monotremes where the. 

 episternum is of large size, and forms a T-shaj)ed 

 'interclavicular' support for the clavicles. We 

 have referred above to one of the chief peculiarities of the pelvis in birds, the forward 

 and backward extension of the ilia and their fusion with the long sacrum. The ventral 

 region also offers many peculiarities, the chief of these being the backward direction 

 of the pubis, and the wide .separation of the ischia. There is consequently no sym]ihysis 

 or epipubis in these forms. Certain fossil Dinosauria have a double pubis, the anterior 

 branch of which appears to be comparable to the pubis of other reptiles, while the pos- 

 tci'ior branch is homologous with the pubis of birds, in which the anterior branch is 

 merely represented by a 'pectineal' process of the pubis. It is fairly certain that the 

 pubis in mammals is likewise comparable to the posterior and not to the anterior branch 

 of the dinosaur pubis, and it is ])ossible that the so-called marsupial bones, well devel- 

 oped in monotremes and marsupials, and present rudimentarily in some higher mam- 

 mals, may be comparable to the anterior branches, and not to the epipubis of other 

 reptiles. 



In adult mammals the three elements of the pelvis unite to form an innominate 

 bone, both the ventral elements of whicli unite in a symphysis in the lower forms, 

 while in the higher forms the pubes alone do so. 



If the anterior and jiosterior extremities of a snapping turtle be comjiared, many 

 points of agreement will be readily detected. Each is divisible into three regions, 

 suppoi-ted by similar bones. Thus in the ))roxim:il region we have the humerus of 



the anterior extremity 

 ie]ii'esented by the fe- 

 mur of the posterior; 

 in the middle region 

 the radius and ulna of 

 the one represented 

 by the tibia and fibula 

 of the other; and in the 

 distal region the skele- 

 ton of the ' man us,' or 

 All of the vertebrates 



Fig. 31. — Fore limb of turtle ; c, centralia ; ca i 

 intermedium; mc i — e^ metacarpals; 7*, radius; 

 uluare ; I— VI, digits, the sixth imperfect. 



hand, containing similar bones to that of the ' pes ' or foot. 



except the fishes are characterized by similarly aiTanged limb skeletons. 



A close insjiection of the manus discloses two rows of small bones succeeding the 

 radius and ulna. These are the proximal and distal carpals, of which nine or ten at 



