359 
also prevents the recti muscles of the eyeball, excepting in part the 
rectus externus, from obtaining suitable origin from the orbital wall, 
and the eyestalk projects forward between the process and the eye- 
ball, nearly to the central point of the latter, to provide that origin. 
The process furthermore, when the eyeball is rotated upward, forces 
the ventral portion of the eyeball outward between the rigid eyelids, 
this giving rise to the protrusion of the eye described by MsRRITT 
Hawkes (1906). 
An orbital process, called by GEGENBAUR the palato-basal pro- 
cess, is said by that author to be found in nearly all selachians, but in 
all the selachians described by him it is not only much less important 
than in Chlamyosdelachus, but it has, in all of them, a more ventral 
articulation with the neurocranium. In the Notidanidae (Hexanchus, 
Heptanchus), where the surface of articulation with the cranial wall 
is relatively large, it lies ventral to the opticus foramen, in the pro- 
jecting ventral portion of the middle of the orbit. In the Spinacidae 
(Seymnus, Acanthias, Centrophorus), where it is still less important, 
it is situated in the ventro-posterior portion of the orbit; while in the 
Carchariidae, Seyllüdae and Rhinidae (Galeus, Mustelus, Prianodon, 
Seyllium, Squatina) it lies in the ventro-anterior portion of the orbit. 
In Cestraeion, the so-called palato-basal articular surface is shown 
by GEGENBAUR anterior to the orbit, but the articulation there shown 
and described is probably not homologous with the palato-basal 
articulation of the other selachians described, for GEGENBAUR says (l.c. 
p. 188) that in Cestracion the palato-basal process is either absent or 
is represented in a slight eminence on the upper edge of the palato- 
quadrate. Beyond this eminence the palato-quadrate is said by 
GEGENBAUR to streteh forward and lie in the groove described by him 
on the lateral surface of the ethmoidal region of the neurocranium. 
In the rays, both the palato-basal process and the articulation of the 
palato-quadrate with the neuroeranium are said to be wholly wanting, 
and this is considered by GEGENBAUR as being due to retrogression. 
PArker’s (1876) descriptions of Raia agree with GeGENBAURr’s, but 
of Seyllium canicula PARKER says that, although the palato-basal 
process is found, it does not articulate with the neurocranium. [he 
process, where found, is always in articular relation with, or in topo- 
graphical relation to, the orbital wall, and hence can properly be 
called the orbital process of the palato-quadrate. 
In Amia and teleosts, the orbital process of the palato-quadrate 
