BLOOD-VESSELS OF MUSTELTJS ANTARCTICUS. 
711 
The jugular vein. 
Internal jugular vein, Monro (16). 
Vena jugularis superior, Muller (17). 
Vena vertebralis anterior s. jugularis, Stannius (25), 
Veines jugulaires, Milne Edwards (14). 
Vena jugularis, Owen (19), Huxley (10), Kolleston (24). 
Jugular vein, Mac a lister (13), Gegenbaur (7). 
As in the case of the carotid arteries {supra, p. 699) there is no precise corre¬ 
spondence between the cephalic veins of fishes and the “ internal ” and “ external ” 
jugulars of the higher animals. In position the vein now under consideration agrees, 
as Monro saw, with the internal jugular, from which, however, it differs in receiving 
the main part of the blood from the whole head, and not only that from the brain. 
The jugular vein (Plate 34, figs. 1 and 2 ; Plate 35, figs. 9 and 10 ; Plate 37, figs. 18, 
26, and 27, Jug. V.) is a very large vessel, about 1 cm. in diameter, and triangular 
in section (fig. 18), situated immediately dorsad of the gills and laterad of the dorsal 
muscles. Anteriorly it lies in the horizontal plane of the auditory capsule (fig. 10), 
posteriorly in that of the oesophagus (fig. 19), so that it takes a direction from its 
cephalic end backwards and slightly downwards. 
At its posterior extremity, as already stated above, the jugular turns downwards, 
caudad of the fifth branchial arch (fig. 10), to enter the precaval sinus, the junction 
between the two being marked by a pair of transversely-placed semilunar valves 
(figs. 2 and 19). 
At its cephalic end the jugular becomes a somewhat irregular channel (fig. 10), 
and passes laterad of the auditory capsule, narrowing considerably in vertical height 
as it does so, and at the same time becoming wider from side to side. It is this 
portion of the jugular which receives the blood from the orbital sinus anteriorly, 
and that of the hyoidean sinus ventrally ( vide infra). Throughout its whole length 
the jugular receives feeders from the dorsal region of the gills and other neighbouring 
parts. 
The orbital sinus. 
Situated within the orbit and surrounding the eye-muscles is a large irregular sinus 
(Plate 35, fig. 10, Orb. S.), always containing more or less blood in the freshly-dissected 
fish. When the eye and its muscles are removed, there is seen, in the posterior wall 
of the orbit, a small depression, bounded externally by a ligament, alongside and 
parallel with which is the hyomandibular nerve or posterior division of the seventh; 
this depression leads by a narrow oblique passage from the orbital sinus into the 
jugular vein, the aperture between the two being guarded by a distinct valve. 
The orbital sinus receives the anterior cerebral vein {infra), and at the anterior 
{inneij canthus of the orbit a vein from the anterior and external region of the head 
