BLOOD-VASCULAR SYSTEM OF THE LORICATI 37 



body. Close to the sinus venosus the right pi"eca\'a receives 

 the inferior jugidar vein (Pis. I and II, figs, i and 12 ; I.J.V.), 

 returnino; the venous blood from the branchial muscles and 

 the pharynx. Passing dorsad around the oesophagus, each 

 precava arises at the ventral surface of the head kidney from 2 

 large trunks ; the cephalic vessels or jugular veins (Pis. I and 

 II, figs. I, 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 (PI. I, figs, i 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 veins 

 (PL I, figs. I and 10; A. and E. Ren. V.) receives blood from 

 the caudal vein (PL I, figs, i 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 auricle or 

 atrium (Pis. I and II, figs, i and 12 ; Aur.), through the ven- 

 tricle (Pis. I and II, figs, i and 12 ; Ven.) into the bulbus 

 arteriosus (Pis. I and II, figs, i and 12 ; B.Art.), from whence 

 it is forced through the ventral aorta or branchial artery (Pis. 

 I and II, figs. I and 12 : V.Ao.) into 4 pairs of afferent 

 branchial arteries (Pis. I and II, figs, i 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 efferent filament 

 arteries (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 (?\s. I and II, figs, i, 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 hyoidean artery (Pis. I and II, figs, i 

 and 12; Hyo.A.) for the hyoid arch and tongue, and which 



