54 ALLEN 
behind the maxilla, and sends one branch ventro-caudad along 
the outer ventral surface of the adductor mandibule muscle. 
As the external carotid artery passes behind the metaptery- 
goid it gives off the large pseudobranchial or afferent pseudo- 
branchial artery (Pl. I, fig. 1; Ps.A.) caudad to the pseudo- 
branchia. Passing behind the hyomandibular, the pseudo- 
branchial artery gives off a good-sized vessel dorsad for the 
levator muscle of the palatine arch, and shortly before the pseu- 
dobranchia is reached the pseudobranchial artery bifurcates 
into a short dorsal branch and a longer ventral branch. ‘These 
vessels are analogous to the afferent branchial arteries of the 
branchial arches. Like them they give off the nutrient pseudo- 
branchial arteries, from which the nutrient filament arteries 
arise for the pseudobranchial filaments (not shown in fig. 3.), 
and at regular intervals an afferent pseudobranchial filament 
artery (il. Li ig..35) a es Hilea.) 1S, given oft ‘to; the outer 
margin of the filament, which is the side that lies closest to the 
hyomandibular bone. As is the case in the branchial filament 
this artery exhausts itself in numerous afferent cross-vessels, 
which by dividing form the vessels from which the fseudo- 
branchial filament network arises. ‘These cross-vessels are much 
shorter than the corresponding branchial vessels and are about 
80m apart, this being 20 more that the distance between 2 
branchial filament cross-vessels. The longest septum of a 
pseudobranchial filament and the inclosed capillary network is 
much longer than the corresponding branchial septum, but the 
network itself is much coarser. In alike manner the capillary 
networks become collected into short cross-vessels on the inner 
side of the filament, which unite in forming the efferent pseudo- 
branchial filament vessels (P\. I, figs. 3 and 4; E.Ps.Fil.A). 
These vessels terminate in, and form a short dorsal, and a longer 
ventral artery, which lie immediately cephalad of the corres- 
ponding afferent vessels, and are analogous to an efferent bran- 
chial artery.’ They unite in forming the important ophthalmic 
'The pseudobranch is a hemibranch or half-gill. Although its capillary net- 
work is a trifle coarser than the network of a branchial filament and its afferent 
vessel comes from the external carotid artery, still it has much in common with 
a branchial filament. The septa containing the pseudobranchial capillaries are 
exposed to the same current of water that bathes the gills, and it is natural to 
