96 
hyoidean artery contributes nothing. In Pleuronectes the 
organ is supplied by the hyoidean artery, and there is no 
evidence of an anastomosis of the latter with the circulus 
cephalicus beyond a doubtful communication between 
branches of the hyoidean and external carotid arteries. 
The Efferent Pseudobranchial Vessel is the ophthalmic 
artery. Blood, after traversing the capillaries in the 
pseudobranchial filaments, passes into this vessel (A.op.), 
which runs forwards along the roof of the pharynx covered 
‘over by the mucous membrane. The two ophthalmic 
arteries approach each other in the middle line of the 
body, then separate and perforate the prootics together 
with the superior jugular veins, passing through the 
jugular foramina (f. jug. fig. 2). Hach vessel accom- 
panies the jugular vein and optic nerve of its side, and 
reaching the eye perforates the sclerotic and breaks up in 
the choroid gland. This peculiar arrangement is common 
to all Teleostean fishes, and has not received any satis- 
factory explanation. Joh. Miiller suggested that the 
pseudobranch was a gland furnishing an internal secre- 
tion, and that the object of the included capillary system 
of the pseudobranch was to equalise the intra-optical 
pressure by smoothing down the pulsations of the heart. 
But the blood in the ophthalmic artery has already passed 
through the branchial capillaries before reaching the 
pseudobranch, and there is no evidence of the elaboration 
of any internal secretion. 
The Pseudobranch.—It will be convenient to give 
some account here of the structure of this organ. It is 
situated on the inner surface of each operculum in a little 
concavity which lies behind the strong transverse muscles 
forming the roof of the pharynx, and which is formed by 
the abrupt termination of these in a posterior transverse 
ridge. It is situated mostly on the hyomandibular, but 
