No. 3.] MORPHOLOGY OF RIBS. 465 
physes move dorsad together with the pleuroids (in this case the 
chevrons cannot represent parapophyses), or the pleuroids alone 
begin to move, separating from the parapophyses, which would 
form the chevrons. The latter opinion was held by me until now. 
The examination of Lepzdosteus shows that this view is incorrect. 
There are forty prze-anal vertebra in a skeleton of Lepzdosteus 
osseus L. before me. From the second we find well-developed 
parapophyses to which strong pleuroids are articulated. In the 
most posterior vertebre the pleuroids begin to bend downwards 
and the parapophyses become a little smaller. The 41st ver- 
tebra shows the following conditions: The pleuroids are con- 
nected with parapophyses and are directed downwards; between 
the two pleuroids a strong element ts placed which nearly touches 
the centrum of the vertebra, and which supports the subcaudal 
blood-vessels ; this strong element ts the first well-developed acti- 
nost of the anal fin. It is very strong proximally, differing from 
the actinosts of other fishes in this regard. In the 42d vertebra 
we have similar conditions. The second well-developed actinost 
is below the vertebra supporting the subcaudal blood-vessels, 
but it is not so strong proximally as the first; the ribs are not 
directed downwards, but backwards, and are entirely separated 
from each other. We have about the same characters in the 
next four vertebrz. In the 43d and 44th the pleuroids are 
turned backwards. The 43d is connected with one actinost, the 
44th with two; the actinosts become very. thin proximally, 
resembling the free actinosts in other fishes. The relation of 
actinosts and vertebrae becomes loose. There are in all eight 
well-developed actinosts of the anal fin; the anterior and pos- 
terior ones are rudimentary ; these eight actinosts are in relation 
to six vertebrz. In the 45th and 46th vertebre the ribs begin 
to turn downwards again, touching each other distally, at the 
same time they enclose the subcaudal blood-vessels. The same 
condition we have in all the following vertebra, in which the 
distal parts of the pleuroids co-ossify and become very strong. 
These distal parts contain also the actinosts of the caudal fin. 
The anterior part of the post-anal portion of the tail in Lept- 
dosteus shows the condition of the higher vertebrates, the posterior 
part that of fishes. 
The Batrachia (Amphibia) developed from forms in which 
the process, which begins at the anterior part of the post-anal 
