BLOOD-VASCULAR SYSTEM OF THE LORICATI 37 
body. Close to the sinus venosus the right precava receives 
the znferzor jugular vern (Pls. I and II, figs. 1 and 12; I.J.V.), 
returning the venous blood from the branchial muscles and 
the pharynx. Passing dorsad around the cesophagus, each 
precava arises at the ventral surface of the head kidney from 2 
large trunks; the cephalic vessels or jugular veins (Pls. I and 
II, figs. 1, 5, and 12; R. and L.J.V.) convey the venous 
blood from the face, nose, eyes, brain, and dorsal branchial 
muscles and their arches; and the caudal vessels or cardinal 
veins (Pl. I, figs. 1 and 5; R. and L.Car.V.) vary greatly in 
length and in size. The short left cardinal returns blood only 
from the left head kidney; while the large right cardinal arises 
in the posterior end of the kidney and through the renal vezns 
(Pl. I, figs. 1 and 10; A. and E.Ren.V.) receives blood from 
the caudal vein (Pl. I, figs. 1 and 10; Cau.V.) coming from 
the tail in addition to collecting blood from the thoracic walls, 
reproductive organs, and viscera. 
From the sinus venosus, the blood passes into the aurzcle or 
atrium (Pls. I and II, figs. 1 and 12; Aur.), through the ven- 
tricle (Pls. I and Il, figs. 1 and 12; Ven.) into the dalbus 
artertosus (Pls. I and II, figs. 1 and 12; B.Art.), from whence 
it is forced through the ventral aorta or branchial artery (Pls. 
I and It, figs: /1-and 12:'V.Ao-) into 4 pairs of afferent 
branchial arterzes (Pls. I and II, figs. 1 and 12; A.Br.A.), 
(the third and fourth pairs, however, arise as one trunk, but 
soon divide), which run in the posterior grooves of their corre- 
sponding arches. These vessels exhaust themselves in numer- 
ous afferent filament arteries (Pl. I, fig. 2; A.Fil.A.), which 
pass along the inner edge of each branchial filament and which 
are collected on the opposite or outer side by the eferent filament 
arterzes (Pl. I, fig. 2; E.Fil.A.), after having passed through 
a fine capillary network, where the blood is purified by the 
oxygen held, physically, in the water. These efferent filament 
arteries, containing pure arterial blood reunite, forming the 
efferent branchial arteries (Pls. I and II, figs. 1, 5, and 12; 
E.Br.A.), which run parallel, but cephalad to the afferent 
branchial arteries. From the ventral ends of these efferent 
vessels are given off the hyordean artery (Pls. I and II, figs. 1 
and 12; Hyo.A.) for the hyoid arch and tongue, and which 
