641 
aorta) while that artery is still on the ventral surface of the chondro- 
cranium, and from this latter artery, or its anterior prolongation the arteria 
orbito-nasalis, two or more branches arise, one of which must certainly 
represent the arteria ophthalmica magna (premandibular aortic arch). 
The arteria ophthalmica magna is not well developed in either 
Amieurus or Polypterus, because of the absence of a choroid gland. 
In Esox, Gadus and the Loricati, on the contrary, this artery is well 
developed, and it has fused, in the adult, at its dorsal end, with the 
dorsal end of the efferent pseudobranchial artery in such a manner 
that the two arteries appear as a single continuous vessel, as I have 
fully explained in my earlier works (Aruıs, 1908a and 1912). Neither 
of these two arteries here falls into either the arteria orbito-nasalis 
or the carotis interna (lateral dorsal aorta), but I found (Auruıs, 1908 a, 
p. 118), in larvae of Scomber and of certain of the Loricati, indica- 
tions of a pre-existing commissural connection, or anastomosis, with 
the orbito-nasalis, which connection I now consider to represent the 
primary connection of these aortic arches with the lateral dorsal aorta. 
The cross-commissural vessel which, in these teleosts, connects the 
ophthalmicae magnae of opposite sides is then simply the commissural 
vessel which so constantly connects the lateral dorsal aortae (internal 
carotids) in selachians, and the anastomosis of the internal carotids in 
teleosts is of secondary origin, as I have already concluded, for other 
reasons, that it must be (Aruıs, 1912, p. 138), and it is in no way the 
homologue of the topographically so similar connection in selachians. 
The arteria optica (centralis retinae) arises, in these several teleosts, 
from the arteria cerebralis anterior, and, according to ALLEN (1905), 
no branch of this latter artery is sent, in the Loricati, to the nasal sac, 
that organ being supplied by branches of the arteria orbito-nasalis. 
Dourn (1886), it is to be noted, does not show an arteria orbito- 
nasalis in either of his figures of embryos of the trout, but as this 
artery is so frequently, if not invariably, found in the adults of other 
teleosts, and as Dourn also does not show either an external carotid 
or a posterior cerebral artery in his figures, both of which arteries 
are found in the adult Salmo (Auuıs, 1912), it seems probable that 
he either overlooked it in his embryos or that it develops relatively 
late in the embryonic life of the fish. 
In selachians and ganoids, and in-Ceratodus, the conditions are 
quite different from those above described, this quite unquestionably 
being related to the amount of the cranial flexure at the time of the 
Anat, Anz. Bd. 46. Aufsätze 41 
