47 G OX OUR PRESENT KNOWLEDGE OF THE ORIGIN OF MAN. 



acteristic and peculiar structure had arisen as they handed down 

 by inheritance to all the sauropsida and mammalia; there is the 

 same shoulder girdle and pelvic girdle, the same simple hollow bones 

 in the upper arm and upper leg, the same pair of bones in the forearm 

 and lower leg, the same complicated union of bones in the wrist and 

 ankle, the same typical arrangement of five fingers and five toes. This 

 striking agreement in the assembling of the bony framework in all the 

 higher four-footed vertebrates struck many thoughtful observers more 

 than a hundred years ago; among others it led our greatest poet and 

 thinker, Goethe, to those remarkable observations on the morphology 

 of animals that we may consider the direct precursors of the modern 

 ideas of Darwin. 



We can, in fact, show, as a certain sign of the derivation of man from 

 the oldest five-toed or pentadactylate amphibians, the fact that we 

 possess to-day on our hand five fingers and on our foot five toes. Man 

 and most primates (not all) show in this and in other respects that 

 through conservative inheritance they have preserved the original plan 

 of structure much more closely than have the majority of other mammals, 

 especially the ungulates. Among others the one-toed horse on the one 

 side and the two-toed ruminants on the other, are much more modified 

 and specialized than are the primates. 



The oldest amphibia of the Carboniferous period, the armored Stego- 

 cephali (and especially the remarkable BrancMosaurid discovered by 

 Credner), are now quite justly considered by all discriminating zoolo- 

 gists as the undoubted common stem group whence were derived all 

 four-footed animals [Tetrapoda or Quadrupeda), all amphibia and amni- 

 ota. But what was the origin of this important group itself? To this 

 question also the great advances of palaeontology afford a satisfactory 

 answer which harmonizes excellently with the older solutions given by 

 comparative anatomy and ontogeny. Already in Jena, forty-four years 

 ago, the first master of comparative anatomy, Carl Gegenbaur, in a 

 series of classical essays, pointed out that the most important parts in 

 the vertebrate skeleton, particularly the skull and the bones of the 

 limbs, reveal to us to-day, in the succession of classes of living verte- 

 brates, a coherent scale of phyletic steps of development. Apart from 

 the more lowly organized Gyclostomata.it is especially the true fishes, 

 and among them again the primitive fishes or Selachians (sharks and 

 rays), which have proved most constant to the original form in the 

 essential relations of their bodily structure. To the Selachians are 

 closely allied the ganoids or enamel fishes, especially the Grossopterygii 

 which take us farther back to the Dipneusta. Among these last the 

 Australian fish Ceratodus has recently become of great interest, its 

 anatomy and ontology having been carefully investigated by G until er 

 and Semon. By this transition group of Dipneusta or amphibious 

 fishes — that is to say, fishes with lungs, but also with fins, with penta- 

 dactylate limbs — is the morphological bridge to the early amphibians 



