higher forms Discosaurus, Petrobates, Hylonomus, Sclerocephalus aud 

 the Labyrinthodontia. 



It is now pretty generally admitted, that the pelvis is a product 

 of the proximal portion of the hind limb, which developes inwards 

 until connection is reached with that of the other side in the median 

 line. The pelvis is complettely chondrogenous, never containing any der- 

 mogenous elements. The most primitive pelvis consists of a median 

 bar of cartilage, to which the limbs are articulated laterally. Sucli 

 pelvic girdles we see for instance in the Elasmobranchii and the Di- 

 pnoi. The pelvic girdle of the fossil Crossopterygians is generally 

 not preserved, in the living forms it seems to be in a rudimentary 

 condition, in Calamoichthys it has even disappeared completely; 

 together with the pelvic fins. The pelvis of the teleostomous ancestors 

 of the Stegocephali must have been formed by a median cartilage with 

 a lateral upper process. The ilium ossified first, than followed the 

 ischium and finally the pubis ; all these elements appearing as centres 

 of ossification in the cartilage. So long as no ossified ventral elements 

 are present yet; the whole cartilage is called gastroid. By the 

 ossification of the pubes and ischia, this cartilage is reduced to an 

 anterior, middle and posterior portion; epi-, meso- and hypo- 

 gastroid. In the Stapedifera we find all the stages, from the pre- 

 sence of these three cartiligiuous elements, to their complete reduction. 

 In some of the Stapedifera there is in front of the epigastroid a spe- 

 cial element, the epi pub is. 



The fore and hind limbs. 



The Stegocephali are the first vertebrates, which possess a cheiro- 

 pterygial limb- like all the classes above fishes. We have in the first 

 segment one element; humerus or femur, in the second two: Radius 

 and Ulna, or Tibia and Fibula. Than follows a series of mesopodials — 

 carpals and tarsals, and finally the metapodials and phalanges. The 

 derivation of the cheiropterygium from the ichthyopterygium is one 

 of the most interesting problems in phylogeny. Formerly the paddles 

 of the Ichthyosauria and Plesiosauria were considered as forming inter- 

 mediate stages; but it has been shown that the ancestors of both Ich- 

 thyosauria and Plesiosauria were terrestrial reptiles with a typical 

 cheiropterygial limb, aud that the paddles were only secondarily de- 

 veloped through adaptation to aquatic life, in the same way as the 

 paddles of the Cetaceans. 



It is the general opinion that the ancestors of the vertebrates 

 with a cheiropterygium, had numerous digits, and there was consider- 



