BLOOD-VASCULAR SYSTEM OF THE LORICATI 89 
the vagus foramen, follows along behind the nerve and receiv- 
ing the much smaller neural vein, penetrates the anterior dorsal 
corner of the head kidney (see fig. 16). Within the head kid- 
ney the posterior encephalic or the most anterior neural vein 
breaks up into very small veins, which again become collected 
and empty into the jugular vein. 
(6) Veens Emptying Directly into the Jugulars. — Under this 
head belong the opercular and the 3 dorsal branchial muscle 
veins. The latter in addition to draining the branchial muscles 
receive also the dorsal nutrient branchial veins from the bran- 
chial arches. In OfAzodon these veins are always present, 
but vary considerably in their distribution. Perhaps the most 
common arrangement is shown in fig. 1. 
Opercular Verns (fig. 1; Op. V.).— These veins arise on 
the inner side of the operculars; running dorsad behind the 
corresponding arteries, they curve ventrad, after leaving the 
dorsal edge of the operculars, and after receiving a branch from 
the levator operculi muscles of Vetter, empty into the jugulars 
a little behind the first dorsal branchial muscle veins. 
Dorsal Branchial Muscle Verns (fig. 1; Br.M.V, only the 
second vein being lettered). — In the specimen from which fig. 
I was drawn, the first of these vessels had its source in, and 
received its principal supply from, the first dorsal nutrient 
branchial vein (fig. 1; D.N.Br.V.). This vessel arises a little 
below the dorsal bend, and is at first the most anterior of the 3 
vessels in the dorsal part of the first branchial arch. In the 
arch it receives a nutrient filament vein (fig. 2; N.Fil.V.), 
coming from the inner margin of each filament. When the 
dorsal bend of the arch is reached, the first dorsal nutrient 
branchial vein crosses over and continues dorsad behind the 
first efferent branchial artery. Then following along the outer 
surface of the first obliquus dorsalis muscle from which it receives 
a branch, it penetrates with the LX nerve through the first levator 
arc. branch. internus muscle, and again crossing over the first 
efferent branchial artery shortly after the carotid is given off, 
finally empties into the ventral side of the jugular a little 
cephalad of the opercular vein. The second dorsal branchial 
muscle vein, in this specimen, takes its source from the union 
