466 BAUR. [Vo.. III. 
portion of the tail in Lepzdosteus, had been carried through the 
whole tail. The form from which the Batrachia started must 
have had a continuous anal and caudal fin, with well-developed 
actinosts free from the ribs. Zhe chevron bones are the actinosts 
of this continuous fin. 
The following diagrams show different vertebrzee from the 
posterior part of the vertebral column in Lepzdosteus : — 
S Q ty y i 
g Y 
I. 2: By 4. 
pf, parapophysis. /, pleuroid. a, actinost. 
I. 40th vertebra of Zepidosteus. 4. 48th vertebra of Lepidosteus. 
2. 4Ist vertebra of Lepidosteus. 5. 53d vertebra of Lepzdosteus. 
3- 43d vertebra of Lepidosteus. 
So far it has been the opinion that the elements of the anal 
and caudal fins of fishes had disappeared entirely in the higher 
vertebrates; but now we have shown that the elements of these 
fins do not disappear, but are represented by the chevron bones of 
the tail vertebra, which are the partial homologues of the actt- 
nosts.| The actinosts of the dorsal fin and the upper part of the 
caudal fin became probably united with the neuroids, and have 
undergone reduction afterwards. That the anterior and posterior 
paired fins of fishes, the anterior and posterior limbs of verte- 
brates in general, are the result of fusion of actinosts of a con- 
tinuous lateral fin, there seems to be little doubt. 
Sept. 19, 1889. 
1 The proximal part of the chevron above the subcaudal blood-vessels represents 
the intercentrum, the distal part the actinost. In all higher vertebrates the intercen- 
trum and the actinost are united. 
