240 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



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). Each 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. Muller 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 



