142 



COMPARATIVE ANATOMY 



H 



The whole arch is, moreover, more strongly ossified, the procoracoid 

 being covered by an investing bone the clavicle, which may 

 more or less completely replace it. This integumentary bone 

 corresponds to the part of the secondary 

 arch which first appears in Ganoids : in the 

 Stegocephali there was a well-developed 

 clavicle connected with the episternum (see 

 p. 44) and peripherally with another bony 

 rod (cleithrum), which also occurred in the 



FIG.IOI.-DIAGRAMOFTHE fossil Reptile Pareiasaurus. 

 GROUND-TYPE OF PEC- Reptiles. As in Amphibians, the most 

 TORAL ARCH MET WITH IN essential parts of the pectoral arch of 



&5SS&SZ Re P tiles . are the . sca P u !\ and coracoid > 



arising in connection with a continuous 



icSlTTta^ ; ^rtilaginous bar or plate, as is well seen in 



scapula. Lizards (Fig. 56). A procoracoid may also 



be formed, and in Chelonians a bone 



usually described as the procoracoid is strongly developed, but 

 is firmly united with the pillar-like scapula, the two being 

 separated from the coracoid by a suture ; hence the bone in 



FIG. 102. PECTORAL ARCH OF THE RIGHT SIDE OF Salamandra maculosa, 

 considerably magnified, and flattened out. 



a, b, bony processes extending into the procoracoid and coracoid respectively ; 

 Cl, procoracoid ; Co, coracoid ; G, glenoid cavity, surrounded by a rim of 

 cartilage (L); S, scapula (ossified); SS, suprascapula. 



question is sometimes spoken of as a proscapula. In other recent 

 Reptiles the procoracoid is much reduced or even absent. 



Traces of the relations of the procoracoid to the clavicle can 

 still be seen in some cases, but the latter, when present, arises 

 mainly from a connective -tissue blastema unconnected with a 

 procoracoid (Fig. 56). Nevertheless a primary and a secondary 

 part of the pectoral arch can also be recognised in Reptiles, the 



