436 Recent Literature. 
alone furnishes data for the elucidation of the subject. Like Eryops 
this genus has five digits on the fore foot. The incomplete remains 
of this genus lead to the conclusion that the Ganocephala pos- 
sesses more elements in both carpus and tarsus than are possessed 
by any other Batrachians (Salamandrella perhaps excepted), and 
that the carpus was very similar to the tarsus. To the Stegoceph- 
ala belong the oldest forms of Batrachia, and in these the number 
of five digits is already usual. The carpus and tarsus of Necturus 
each consist of six elements in the adult ; while in Cryptobranchide 
(Urodela), both in the American and Asiatic species, the carpus has 
eight, and the tarsus ten elements. The author puts into tabular 
form the various changes which occur in the number of the ta 
and carpal bones during growth, and gives examples drawn from 
all the urodelous families, characterizing each primitive element by 
a letter or number, and tracing the separations and incorporations 
of each with its neighbors. ‘These tarsal and carpal tables are 
followed by a table of the number of the digits in various existing 
and extinct Batrachia. The rudiment of a sixth digit occurs in 
the Cryptobranchidz and Amblystomide. 
Of the three possible modes of origin of the digitated limb 
(Cheiroterygium): from the fin-form, viz., development from a 
many-rayed fin; development from a few-rayed fin that has been 
formed by the obsolescence of the greater part of the rays of a 
many-rayed fin; and entire sprouting off from a form which had 
entirely lost its finned extremities. Dr. Baur declares that neither 
embryology nor palzontology are favorable to the first. All that 
can be asserted with precision regarding the ancestral form of the 
Stapedifera is, says our authority, that, since all save strongly mod- 
ified members of this group have a single bone in the first series of 
the limbs (humerus, femur), and two bones in the second series 
(radius, ulna ; tibia, fibula), so the ancestral form must also have 
had a single ray in the first series, and two rays in the second 
series. If the two rays of the ancestral form ended each in a single 
ray, the remaining three digits of the pentadactyle extremity must 
have been developed by sprouting ; but if the primitive form pos- 
sessed five digits, the remaining three must represent the last 
remains of a many-rayed fin. As facts which seem to lend sup- 
port to the sprouting theory (already advanced by Bruhl) Dr. Baur 
instances: (1) the secondary division of the rays of the Ichthyop- 
terygia ; (2) a case of the division of the one-rayed fin of Protop- 
terus, noticed by Albrecht ; (3) the development and regeneration 
of the extremities of the Urodela. When the development of the 
fins of Ceratodus and Protopterus have been studied ; when that of 
such extremities as normally possess two centralia has been wor 
out; and when the few-toed extremities of Proteus are fully 
understood, a great step will have been made towards the solution 
of the problem. The treatise of Dr. Baur is the most complete 
