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 
Ist efferent vessel and runs backwards and downwards 
among the muscles of the Ist 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 Ist and 2nd efferent vessels. 
Apparently they do not anastomose in Pleuronectes. The 
first, which is the hyoidean artery (A. Ay.), 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 Vessel.—The precise 
disposition of the afferent pseudobranchial vessels varies 
among T'eleostean 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 
deseribed another in //sov, 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., 9 Bd., pp. 229-252, 1883-4. 
