374 H. H. SWINNERTON. 
In the adult sturgeon the metapterygium lies almost in the 
region where the base of the fin passes into the body-wall, 
and has not yet rotated much outwards to form part of the 
free fin. It thus occupies the same position as the process. 
It is significant that in the Ganoids which possess a meta- 
pterygium, development, so far as known, has revealed no 
postcoracoid process. In the Teleosts, which have no meta- 
pterygium, the process is very generally present, and present 
in widely diverse types. 
The fact that the process is continuous with the girdle is 
not a serious objection to the view, for in early development 
the radials are continuous with one another and with the girdle. 
This view does not agree with Gegenbaur’s conclusion 
(p. 161) that the metapterygium of Ganoids has become one 
of the radials of the Teleosts. Based, as it is, upon the 
study only of adult living forms, his conclusion is so far sound. 
But all diversities of structure are not wrapped up in 
Lepidosteus and Amia. Other types have existed, and 
many facts of Teleostean morphology will probably find their 
explanation only among them. 
The Evolution of the Pectoral Skeleton of 
Teleostomes. 
At its first appearance the pectoral skeleton of the sturgeon 
consists of five short rays and a plate, the “ primires basale.” 
From Mollier’s figures it is evident that the line of attach- 
ment of the rays to the plate is parallel to the long axis of 
the body. The skeleton at this stage, then, bears a close 
resemblance to the pelvic skeleton, and presents such a con- 
dition as the fin-fold theory of the origin of paired fins 
requires. Mollier tells us that the second to the sixth spinal 
nerves converge to the “ primires basale,” and bifurcate 
medially to it, sending one branch to the dorsal and the other 
tothe ventralside. In the adult (Pl. 23, fig. 15) the second and 
third nerves, united with a branch from the hypoglossal or 
first spinal, form a common trunk (n. 1—3), which bifurcates 
