BLOOD-VASCULAR SYSTEM OF THE LORICATI gi 
3. Infertor Jugular Veins. 
These vessels return the venous blood from the ventral mus- 
culature of the head, heart, and ventral portion of the branchial 
arches and correspond in the main to the pharynx artery. The 
inferior jugular vein, however, does not become a paired vessel 
until near its termination in the precaval vein. 
The inferior jugular vein may be said to arise from a small 
vein coming from the ventral surface of the tongue, the Zngual 
ven (Pi We tier; lin. V.). This'vein continuing’ caudad 
as the inferior jugular vein, passes in a median line above and 
between the hyohyoideus superior muscles, after which it re- 
ceives 3 pairs of veins, the first pair coming from the outer 
posterior surface of the geniohyoideus muscles, the second from 
the inner surface of the hyohyoideus superior muscles (Pl. I, 
fig. 12; Hys.V.), and the third pair are the ventral nutrient 
branchial veins from the first branchial arch. The latter ves- 
sels (Pl. Il, fig. 12; N.Br.V.) drain the ventral half of the first 
pair of arches. Each of them arises as a paired vessel in front 
of the first efferent branchial artery. The nutrzent filament 
veins (Pl. I, fig. 2; N.Fil.V.) from one side empty into one of 
these branches and those from the opposite side into the other 
branch.’ Further caudad these two branches unite forming a 
single nutrient branchial vein into which a few of the most 
ventral nutrient filament veins from both sides are poured. In 
front of this nutrient branchial vein, running along the cephalic 
margin of the arch, is another vein, which sends caudad cross- 
vessels that empty into the main ventral nutrient branchial vein. 
Continuing ventrad, cephalad of the efferent branchial trunk, 
the first ventral nutrient branchial vein empties into the inferior 
jugular vein. After collecting these veins the inferior jugular 
passes caudad, above the thyroid gland and the ventral aorta; 
receiving branches from the gland, other ventral nutrient branch- 
ial veins, and several small veins coming from the obliqui ven- 
trales muscles. Emerging from the last pair of afferent bran- 
chial arteries the inferior jugular continues caudad, passing 
1 Tt is of interest to note that the nutrient filament veins come-from the inner 
margins of their filaments; while the nutrient filament} arteries are distributed 
to the outer margins. 
