54 ALLEN 



behind the maxilla, and sends one branch ventro-caudad along 

 the outer ventral surface of the adductor mandibul^e muscle. 



As the external carotid artery passes behind the metaptery- 

 goid it gives off the large -psetidobranchlal or afferent pseudo- 

 branchial artery (PL I, fig. i ; 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 (PI. I, fig. 3 ; A.Ps.Fil.A.) is given off 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 -pseudo- 

 branchial filament network arises. These cross-vessels are much 

 shorter than the corresponding branchial vessels and are about 

 80 /A apart, this being 20 \i 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 (^\. 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 arterj', 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 



