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slightly posterior to the pituitary fossa there curves upward and ends 
at the summit of the postelmoid wall, as Goopry has stated. Imme- 
diately posterior to this point, in the one specimen that was alone 
examined in this respect, there was a small median conical pit in the 
floor of the cranial cavity. This pit was directed ventro-poste- 
riorly, and from the apex of the pit a line of soft tissue, somewhat 
membranous in appearance, ran posteriorly, slightly dorsal to the 
notochord, until it reached a point about half way to the hind end of 
the ehondrocranium, where it rose close to the dorsal surface of the 
cartilage of the basis cranii and vanished. Into the apex of this pit 
a small canal led, on either side, from the anterior surface of the 
postelinoid wall, and it may be that it was this condition of the carti- 
lage here that led Ayers (1889) to conclude that the cranial aorta of 
his deseriptions here entered the pituitary fossa. The significance of 
the little pit could not be determined, but it would seem as if the line 
of tissue extending posteriorly from it must represent a persisting 
remnant of the ligamentum longitudinale dorsale inferius of the 
vertebral column: and if this be so it would seem as if the tissues 
that ultimately give rise to the roof of the myodome of ganoids and 
teleosts, might be tissues derived from, or related to, an anterior 
prolongation of this ligament. 
From the lateral end of the postelinoid wall a large low swelling 
runs dorso-antero-laterally, on either side, and vanishes at about 
the middle of the height of the lateral wall of the cranial cavity. It 
lies between the foramen trigeminum, posteriorly, and the opticus, 
oculomotorius, pituitary and efferent pseudobranchial foramina 
antero-ventrally, thus having the position of the alisphenoid cartilage 
of Szewerrzorr’s (1889) descriptions of embryos of Acanthias and 
Pristiurus. GEGENBAUR describes this swelling (Wulst), or ridge, 
in certain selachians, and he says that it lies between the middle and 
posterior regions of the cranial cavity. Its postero-ventral portion, 
in Chlamydoselachus, has the position of the pila prootica of Gaupp’s 
(1900) descriptions of Lacerta, the slight swelling that, in Chlamydo- 
selachus, extends dorso-posteriorly from the lateral edge of the pre- 
sphenoid bolster having the position, relative to the foramina opticum, 
oculomotorium and trochleare that the pila metoptica has. ‘The 
region occupied, in Lacerta, by these two pilae and the intervening 
fenestra metoptica is thus, in Chlamydoselachus, a continuous carti- 
laginous wall and it is perforated not only by the foramina for the 
