BLOOD-VESSELS OF MUSTELUS ANTARCTICUS. 
713 
The chief tributaries of the hyoidean sinus are— (a) veins from the mandible 
entering its ventral or submental portion ; (/>) several nutrient veins from the 
hyoidean hemibranch (fig. 10, Nu. hy. V.) ; and (c) a vein (Post. fac. V.) entering 
near the junction of the hyomandibular and cerato-hyal which I have been able to 
trace only for a very short distance ; probably it is safe to call it the posterior 
facial vein. 
The inferior jugular vein. 
A small vein somewhat like to our anterior external jugular, Monro (16). 
Vena jugular is inferior, Muller (17), Stannius (25). 
The inferior jugular veins (Plate 34, figs. 1 and 2 ; Plate 35, fig. 10 ; Plate 37, figs. 18, 
26, and 27, Inf. jug. V .) are moderately-sized vessels, lying, one on each side, at the 
base of the gills, about 1-2 cm. laterad of the ventral aorta. Each anastomoses 
in front with the corresponding hyoidean sinus, and passing backwards, receives the 
nutrient veins of the four holobranchs. After receiving the last of these, the inferior 
jugular is deflected somewhat outwards and comes to lie in the roof of the pericardial 
cavity immediately mesiad of and parallel with the fifth cerato-branchial, finally 
entering the precaval sinus by the aperture already noticed. 
In an embryo of Scymnus licliia, referrable to “ Stage O ” of Balfour (1, Plate VIIL, 
figs. O, O'), the inferior jugulars are already large vessels, and, along with the 
jugulars, open by wide valveless apertures into the short precaval sinuses (Plate 37, 
figs. 27 and 27). 
The nutrient branchial veins. 
Venae bronchioles, Muller (17). 
Veines cle Duvernoy, Milne Edwards (14). 
Of these there are four on each side, one for each holobranch (Plate 34, fig. 2 ; 
Nu. Br. V., 1-4). The first three are similarly situated, being parallel to the ventral 
portion of the extra-branchial cartilage and to the nutrient branchial artery ; in each 
case the vein is anterior, the cartilage posterior, and the artery intermediate in 
position. The fourth nutrient vein takes a somewhat different course, lying mainly 
on the posterior face of the gill. They are connected with a rich plexus of veins. 
4 Y 
MDOCCLX XXVI. 
