95 



ventrally among the muscles on the anterior border of the 

 pericardium, where it apparently breaks up : a much 

 smaller vessel takes origin from the dorsal portion of the 

 1st efferent vessel and runs backwards and downwards 

 among the muscles of the 1st and 2nd gill arches, where 

 it breaks up. These vessels are represented but not 

 lettered in fig. 22. 



Two fairly large trunks take origin on each side from 

 the ventral portions of the 1st and 2nd efferent vessels. 

 Apparently they do not anastomose in Pleuronectes. The 

 first, which is the hyoidean artery (A. hi/.), leaves the 

 efferent trunk while still within the arch, and after giving 

 off a small twig, which breaks up on the internal surface 

 of the operculum, turns round dorsally and runs on the 

 internal surface of the operculum externally to the cerato- 

 hyal and symplectic bones. At the level of the upper 

 extremities of the gill arches it breaks up into a number 

 of branches which end in the filaments of the pseudo- 

 branch (Ps. Br.). 



The Afferent Pseudobranchial Yessel.— The precise 

 disposition of the afferent pseudobranchial vessels varies 

 among Teleostean fishes. In the greater number the 

 afferent vessel is the hyoidean artery, which, moreover, 

 anastomoses with the circulus cephalicus, so that the blood 

 in the minute vessels of the pseudobranch may be derived 

 from that in all the efferent branchial vessels. This is 

 the arrangement in Gadus. In others, of which Salmo is 

 an example, the hyoidean artery is the sole afferent vessel, 

 and does not anastomose with the circulus cephalicus. In 

 addition to these types of blood supply, Maurer* has 

 described another in Eso.v, where the afferent vessel of the 

 pseudobranch is a twig of the circulus cephalicus and the 



* Beitr. zur Kenntniss der Pseudobranchien der Knochenfische, Morph. 

 Jahrb., 9Bd., pp. 229-252, 1883-4. 



