22 Macuieay Memorian Vouume. 
The anterior cardinal system is composed of the following veins :— 
(1) Superior jugular veins (figs. 8, 15, and 16). 
These are a pair of large vessels entering the Ductus Cuvieri, one on each side. The 
latter run outwards from the heart and at the same time take a forward and slightly 
downward course towards the wall bounding posteriorly the gill cavity. In this way 
each comes to lie close underneath the upper part of the coracoid of its own side. 
Here it receives the inferior jugular vein and a large branch which curves backward 
for a very short distance and is formed by the union of four other veins. The 
relation of these is shown in figs. 8, 15, and 16. One of the four is the large jugular 
vein (sup. jug.) which from this point runs upwards, slightly forwards and inwards, 
till it reaches a position above and behind the gill arches and close to the anterior 
border of the upper extremity of the supra-scapula. At this point it receives a 
number of small branches, (a) from the muscles lying immediately posterior to the 
supra-scapula, (b) from the muscles on the dorsal surface just behind the skull, 
(c) from the muscles on the dorso-lateral aspect of the head above the gill cavity 
and (d) from the region of the gill arches. 
From this point the vein runs in a direction which hes roughly at right angles 
to that of its proximal part: it turns forwards almost parallel to the long axis of the 
body, runs horizontally above the level of the arches and pierces the cartilaginous 
cranium in the auditory region. Here it runs dorsad of the branches of the ninth 
and tenth cranial nerves as they pass outwards to the gill arches but ventrad of the 
connecting branch between the seventh and ninth nerves. Dipping ventralwards it 
passes beneath the outer part of the auditory organ and then gradually rising dorsal- 
wards runs forward beneath the anterior and posterior carotids till it reaches the 
level of the apposed fifth and seventh nerves. Beyond the main stem of the fifth 
nerve it rises towards the dorsal surface and at the level of the orbit emerges from 
the cartilage and opens into a large sinus-like space beneath the temporal muscles 
which are covered over externally by the supra-orbital bone. 
From this sinus five other sinus-like vessels diverge (fig. 15) :-— 
(1) One towards the mid line anteriorly, into the lower layer of muscles. 
(2) One almost directly dorsalwards into the upper layer of muscles immediately 
beneath the supra-orbital. 
(3) One to the orbit where it forms the orbital sinus. 
(4) One running slightly posteriorly and upwards to the mid dorsal line, where 
it is In connection with a similar vessel from the other side. 
