243 
The efferent pseudobranchial artery, in Lepidosteus, runs upward 
antero-mesial to the basipterygoid process, and without perforating 
the cartilage of the cranial wall at any point falls into the internal 
carotid artery while that artery is still on the ventral surface of the 
chondrocranium in a canal that lies between that surface and the 
underlying parasphenoid. The efferent pseudobranchial artery of 
Lepidosteus differs in this from the artery in all of the selachians that 
I have examined, and also from that in Amia; and it is probable that 
in most teleosts the conditions are comparable, though not exactly 
similar to, those in Amia (Atuis, 1909). In Polypterus (Auxis, 1908 a) 
and in Ameiurus (Autts, 1908b), on the contrary, the efferent pseudo- 
branchial artery falls into the internal carotid external to the chon- 
drocranium, as it does in Lepidosteus; and it is to be noted that in 
both these fishes the myodome is in the same undeveloped condition 
that it is in Lepidosteus, and that in Ameiurus there is apparently no 
trigemino-facialis chamber (Auuis, 1908b). 
The trigemino-facialis chamber of Lepidosteus is traversed its full 
length by the internal jugular vein, as I find by now reexamining my 
sections. The ramus palatinus pierces the floor of the chamber, and 
the external carotid artery enters the chamber by this palatinus 
foramen and issues from the chamber by its orbital opening (Auuıs, 
1909). The chamber has, in the adult, a bony mesial wall, and Vzrr’s 
descriptions of embryos would seem to indicate that this wall corre- 
sponds to the mesial membranous wall of the acustico-trigemino- 
facialis recess of Chlamydoselachus. If this be so, it is evident that 
the lateral wall of the recess of Chlamydoselachus has been resorbed 
in Lepidosteus, and that the recess itself, as well as the several separate 
canals that, in selachians, together represent the as yet undeveloped 
trigemino-facialis chamber have, in Lepidosteus, fused to form a 
single large chamber which is a strictly intramural space. 
The trigemino-pituitary fossa of selachians is represented, in 
Lepidosteus, in the space that overlies the basal portion of the basi- 
pterygoid process, that process evidently representing the floor of 
the selachian fossa together with some part of the subocular shelf 
of Acanthias. A myodome has not yet been developed. 
The notochord, in the 149 mm. specimen of Lepidosteus, is said 
by Veır to end, anteriorly, slightly posterior to the cavum sacci 
vasculosi and to there perforate the cartilage of the basis cranii and 
become exposed on its ventral surface. In my 80 mm. specimen the 
16* 
