156 THE ANATOMY OF YERTEBRATED ANIMALS. 



and there can be little doubt that the other Labyrinthodonta 

 resembled it in this respect. 



The limbs and their arches are completely absent in the 

 Gymnopliiona^ and, apparently, in the extinct Ophiderpeton 

 of the Carboniferous formation. In all other Amphibia the 

 pectoral arch and limbs are present, and, in all but Siren, the 

 pelvic arch and limbs. The anterior and j^osterior limb-arches 

 consist of a continuous cartilage on each side, divided by an 

 articular surface into a smaller dorsal moiety, and a more ex- 

 panded ventral portion. The dorsal moieties are, respectively, 

 the scapula and the ilium. The ventral moieties are divided 

 by notches, or fontanelles, into two portions — an anterior, pre- 

 coracoidal, or pubic part, and a posterior, coracoidal, or ischial 

 part. 



In the TIrodela the scapula ossifies, and its ossification may 

 be prolonged into the coracoid and precoracoid, but there is 

 never more than one osseous mass. The clavicle is not devel- 

 oped. In Siredon, the Derotremata^ and Scdamandridea, the 

 coracoids are received into grooves of the anterolateral edges 

 of a cartilaginous sternum. 



The pectoral arch of the Labyrinthodonts seems to have 

 possessed representatives of clavicles in the lateral thoracic 

 shields. The structure of the rest of the arch is not clear, but 

 ossified coraco-scapular pieces seem to have existed. 



In the Satrachia^ the coraco-scapular cartilages are some- 

 times, as in the common Frog, firmly united in the middle 

 line, and send forward a median process, which becomes ossi- 

 fied, and is the omosternvm (Fig. 57, o.st.^. Behind, the cora- 

 coids articulate with a well-developed sternum (5^.). Distinct 

 ossifications arising on either side of the glenoidal cavity rep- 

 resent the scapula (^c.) and the coracoid {cr?), and the upper 

 moiety of the scapula may be distinctly ossified as a supra- 

 scapula [s.sc). The coracoid is divided by a large membra- 

 nous space ov fontanelle into a proper coracoid (cr.), which lies 

 behind the fontanelle ; a persistently cartilaginous epicoracoid 

 {e.cr.), which bounds it internally ; and a precoracoid, which 

 limits it in front. Closely applied to the precoracoid is an 

 ossification in membrane, which represents the clavicle. 



The pelvic arch is attached (except in Proteus) to the ex- 

 tremity of the sacral rib. An iliac ossification is always devel- 

 oped ; an ischial, in all but Proteus. The pubis does not ap- 

 pear to be regularly represented by a distinct ossification. In 

 the Patrachia the applied flat faces of the expanded ventral 

 divisions of the pelvic arch coalesce into a disk. 



