Raymond C. Osburn fA 
argument but merely indicate still more clearly the exceedingly close 
relationship which exists between the paired and median fins. The serial 
homology of limb girdles with gill-artéhes is shown to be impossible, and 
the trapezial connection can only be secondary. The branching carti- 
lages observed in the hyoid region are to be regarded only as parallel- 
isms,—produced probably by similar causes to those which have been 
operative in producing the fusion of rays to form basalia in the fins. 
Concentration or abbreviation of the region at base of the radii would 
seem sufficient to cause this in either fin or gill. 
On the other hand, the manner of development of the pectoral girdle 
proves it to have been derived through a type similar to the pelvic, 
showing the latter to be the more primitive in form, while proof is not 
wanting to show the connection between basalia (girdles included) of 
paired and unpaired fins. The study of the earliest conditions in the 
formation of the inferior caudal places this fin on the same basis as the 
others and indicates the similar external origin of all. When we con- 
sider, in addition to the foregoing points, the exactly similar origin and 
development of the muscles, nerves, blood-vessels, and ceratotrichia in 
both kinds of fins, the case becomes so strong as to appear a certainty. 
I think we may safely conclude that the external or fin-fold origin of the 
paired limbs is clearly demonstrated, at least as fully as is possible until 
paleontology shall reveal the whole story by supplying the absolute serial 
stages in the evolution of these organs. 
CoLUMBIA UNIVERSITY, 
March 9, 1907. 
LIST OF PAPERS REFERRED TO. 
Batrour, F. M., 78.—A Monograph on the Development of Elasmobranch 
Fishes. Journ. Anat. and Physiol., 1876-78. 
81.—On the development of the paired fins in Elasmobranchii, consid- 
ered in relation to its bearings on the nature of the limbs in Verte- 
brates. Proc. Zool. Soc., London, 1881. 
Bravus, H., 98.—Ueber die Innervation der paarigen Extremitaten bei Sela- 
chiern, Holcephalen und Dipnoern. Ein Beitrag zur Gliedmassen- 
frage. Jena. Zeitschr. Naturw., Bd. XXXI (N. F. 24), 1898. 
o4a.—Tatsachliches aus der Entwickelung des Extremitatenskelettes 
bei den niedersten Formen. Zugleich ein Beitrag zur Entwickel- 
ungsgeschichte des Skelettes der Pinnae und der Visceralbogen. 
Jena, 1904. Festschrift zum Siebzigsten Geburtstag von Ernst 
Haeckel. 
