664 



to small haemapophyses. In all the Vertebrata the lower arches' in 

 the tail are haemapophyses. In the Teleostomi they become in the 

 anterior region the haemal ribs. In the Amphibia and Amiiiota we 

 find in the tail haemapophyses and pleurapophyses, in the precaudal 

 region only pleurapophyses, the haemapophyses having been reduced. 

 The ribs of the Teleostomi are therefore not homologuous to the ribs 

 of the Stapedifera (Batrachia plus Amniota) ; the Teleostomi have 

 lower ribs (haemal arches) ; the Stapedifera upper ribs (pleural arches). 

 In Polypterus of the Crossopterygii we find, that both the upper and 

 lower ribs are present simultaneously. The upper ribs or pleural 

 arches are much stronger than the lower ribs (haemal arches) and 

 are connected with well developed diapophyses. The lower ribs are 

 slender and form the haemapophyses in the tail. The Batrachia must 

 have developed from Crossopterygia, in which the lower ribs in the 

 precaudal region became reduced. The condition of the ribs (haemal 

 arches) in the Dipnoi, alone is sufficient to refuse completely the 

 opinion of the origin of the Batrachia (Stegocephalia) from the Dipnoi. 

 Among all Teleostomi only Crossopterygii can be con- 

 sidered as ancestral to the Batrachia. These point were 

 fully brought out as early as 1853 by August Müller, and he makes 

 the very pertinent remark: "The ribs of Lepidosiren (Dipnoi) become 

 the lower arches (haemal arches) in the tail, therefore the Lepido- 

 sirens are fishes." The ribs of the o-ldest Batrachia, the 

 Stegocephali are not homologuous to the ribs of the 

 Dipnoi; therefore the Dipnoi can not be the ancestors 

 of the Stegocephali. 



The shoulder girdle. 



The shoulder girdle of the Stegocephali consists of two ditterent 

 components exactly as in the case of the skull. We have a chondro- 

 genous portion represented by the scapula and coracoid, and a dermo- 

 genous portion, the iuterclavicle the clavicles, and the cleithrum 

 (Gegenbaur). 



The true nature of the cleithrum which hitherto has always 

 been considered either as a scapula, precoracoid or clavicle has been 

 determined lately by Gegenbaur in a most interesting paper, published 

 in the Morphologische Jahrbuch (Vol. XXIII). In the Stegocephali 

 the dermal are much more developed than the cartilaginous elements. 

 We have seen that the osseous dermal plates of the skull were the 

 product of the union of placoid scales; the same must be true for 

 the dermal bones of the shoulder girdle. In the Elasmobranchii the 



