with Gaupp’s statement of the characteristic relations of the nerves 
to the process and is hence perhaps in error. WIEDERSHEIM then 
adds that GEGENnBAUR has shown that similar conditions are found 
in many selachians. But WIEDERSHEIM and Gavupp were doubtless 
at the time both unaware of the fact that the foramen that is said 
by GEGENBAUR to give passage to the first branch of the trigeminus 
(Ramus ophthalmicus) certainly does not, in every case, give passage 
to the ramus opthalmicus profundus trigemini, which nerve is the 
homologue of the first branch of the trigeminus, or orbito-nasalis, of 
amphibians. For both Tırsına (1896) and I (1901) have shown that 
the ramus profundus issues from the neurocranium, in Mustelus, by 
a wholly separate and independent foramen which lies nearer to the 
trigeminus foramen than to the ophthalmicus foramen. 
It is accordingly quite certain that the bridge of cartilage above 
referred to in selachians does not represent the ascending process of 
amphibians, and I would suggest that the homologue of that process 
is the selachian eyestalk and that that eyestalk is a modified branchial 
ray or rays, of a mandibular or premandibular arch, that has secon- 
darily acquired relations to the eyeball. This eyestalk is, in all selachi- 
ans, attached by one end to the orbital wall, the attachment being such 
that GEGENBAUR considered it as secondary. The other end of the 
eyestalk gives support to, but is not attached to the eyeball, and this end 
of the stalk, in Chlamydoselachus, lies close to if not actually in contact 
with the dorso-mesial edge of the palato-quadrate. If an attachment 
were to be acquired here, which would be a normal relation if the 
stalk is a branchial ray, and if the other end of the stalk were to travel 
upward along the orbital wall, passing between the foramina that give 
exit to the ramus ophthalmicus profundus and the truncus maxillo- 
mandibularis trigemini, the relations of these nerves to the process, 
found in urodeles, would arise. The relations of the veins and arteries 
of the orbit to the stalk and process would apparently also be similar 
in the two cases, but those of the oculomotorius and abducens nerves 
would be quite different. 
In Mustelus, both Trestne and | found the superior division of 
the nervus oculomotorius running directly forward from its foramen 
to the muscles it innervated, while the inferior division of the nerve 
ran postero-laterally above the eyestalk and then forward below it. 
The stalk, in Mustelus, thus lies between the two divisions of the nerve, 
and it is evident that no simple shifting of the point of attachment of 
