644 ALLENS. [Vou. XII. 
apparently attached to, or in any way directly connected with, 
the epidermis. It extends, in embryos, approximately from the 
level of the dorsal end of the second arch backward, above and 
beyond the dorsal ends of the other arches, onto the outer sur- 
face of the front edge of the supraclavicular. A large venous 
vessel lies at first immediately dorsal to it, and then immedi- 
ately internal to it, but in the purely superficial examination 
that was made no branches were found leading into it. 
There is no hyoidean demibranch or opercular gill, but there 
is a well-developed pseudobranch, lying in what Wright has 
called the pseudobranchial canal (No. 133, p. 493). 
a. Basal Line. 
Between the distal ends of the branchial arches there is a 
median line of basal elements, three in number in the adult 
(BB'-3, Figs. 49-51, Pl. XX XIII). 
The first of these elements is as long as, or a little longer 
than, the other two together, and is, in its middle portion, 
ossified, the ossified portion lying between the ventral ends of 
the second and third arches. The other two elements are 
entirely cartilaginous, and it is perhaps worthy of note that 
the single piece of bone in the entire line gives no direct 
attachment either to the arches themselves or to the muscles 
of the arches. In Lepidosteus the corresponding portion of 
the basal line is also osseus (No. 129, p. 272). 
The anterior cartilaginous portion of the first element is, 
roughly speaking, square in section. It is longer than either 
of the other two portions, and has a deep transverse fissure 
across its ventral surface near its front end. The part in front 
of this fissure is considered by van Wijhe as the basihyal partly 
fused with the first basibranchial. On its anterior face, extend- 
ing close to the median line, it has two deep depressions in 
which it receives the articular ends of the hypohyals. Imme- 
diately behind the fissure, beginning in it and extending 
upward and backward transversely across the element, there 
is on either side a deep articular cup for the articular end of 
the first hypobranchial ; and immediately in front of the 
