HYOMANDIBULA OF THE GNATHOSTOME FISHES 589 
have secéndarily acquired attachment to the neurocranium dor- 
sal to the vein. The ligament would in either case have lain 
primarily ventral to the nervus hyomandibularis facialis and 
hence when it had secondarily acquired attachment to the neuro- 
cranium it, would lie anterior to that nerve. . 
In the Batoidei the conditions are markedly different from 
those in the Selachii. 
Gegenbaur (’72) considered the hyomandibula of the Batoidei 
to be the strict homologue of that of the Selachii, the epihyal of 
his descriptions of the adult being formed by secondary segmen- 
tation from the dorsal end of the ceratohyal, and the pharyngo- 
hyal, where found, by segmentation from the dorsal end of the 
so-formed epihyal. 
Parker, in his work published in 1876, says (p. 220) that the 
hyomandibula of Raia is formed by one half only of the epihyal, 
the primarily continuous cartilaginous bar of the hyal arch hay- 
ing been cleft obliquely, from the middle line upward and back- 
ward, instead of transversely at the middle line as in the Se- 
lachii. The anterior segment so cut off formed the hyomandibula 
and the postero-inferior one a bar which later segmented trans- 
versely into the definitive epihyal and ceratohyal. Parker (p. 
214) calls this remaining, postero-inferior portion of the entire 
bar, before its secondary segmentation, the styloceratohyal, but 
as it is said to segment into an epihyal and a ceratohyal, it is not 
clear whether or not he intended to homologize the definitive so- 
called epihyal of the Batoidei with the stylohyal of the Teleostei. 
Parker repeatedly says, in this work, that no pharyngeal element 
is developed in the hyal arch of the Batoidei. But, in a footnote 
in a later work (’82, p. 147), he says of these fishes that ‘‘the 
metapterygoid and hyomandibular naturally classify themselves 
with the succeeding pharyngo-branchials;”’ which is not at all in 
accord with his earlier statements, and, as he makes no reference 
to those earlier statements, it is again not clear just what his 
opinion was. 
Dohrn (’85) considered the hyomandibula of the Batoidei to 
belong to a visceral arch between the hyal and mandibular 
arches, and it is probable (1. c., p. 82) that he considered it to 
