BLOOD-VESSELS OF MUSTELUS ANTAROTICUS. 
715 
thin sections of the pelvic region, that the adult condition of things is already 
fully established. 
Tracing the cardinals forward from the point of union of the left with the 
right, each is seen to dilate into a large cavity, the cardinal sinus (Plate 34, 
figs. 1 and 2; Plate 35, figs. 9 and 10; Plate 37, figs 19-2 L, Card. S.) which 
opens into the corresponding precaval sinus as already described (p. 710). The 
two cardinal sinuses communicate with one another by a wide oval aperture (fig. 
10, ap.) close to the entrance of the spermatic vein ( Sperm. V.). 
The cardinal veins receive the efferent renal veins from the kidneys, and, in the 
anterior half of the abdomen, the oviducal and the spinal (segmental) veins. The 
posterior oviducal and spinal veins, as already stated, open into the renal portal 
veins. 
The spermatic vein. 
This (Plate 34, fig. 1, Plate 35,fig. 10, Sperm. V.) is a very large and capacious vessel, 
deserving rather to be called a sinus than a vein in the adult. It receives the blood 
from all but the posterior extremity of the ovary or testes (see p. 707), and opens into 
the conjoined portion of the cardinal sinuses. Close to its entrance the spermatic 
vein receives the large anastomotic trunk (y) from the anterior lieno-gastric vein 
(supra, p. 708). 
The posterior cerebral and myelonal veins. 
The veins from the anterior part of the brain, i.e., as far back as the mesencephalon, 
have been seen (p. 712) to pour their blood, by the symmetrical anterior cerebral veins, 
into the orbital sinuses. The veins from the cerebellum and medulla oblongata unite 
to form on each side a posterior cerebral vein (Plate 35, fig. 8, Post, cereb. V.), which 
lies dorso-laterad of the medulla. About 0*5 cm. caudad of the calamus scriptorius 
the two posterior cerebral veins unite with one another, on the dorsal surface of the 
spinal cord, to form the myelonal vein (Myel. V.) which extends backwards along the 
whole length of the cord. In each vertebral segment this vessel forms a small simple 
rhomboidal plexus, from the lateral angles of which commissures are given off, and, 
passing outwards and downwards, discharge into either the jugular, the cardinal, the 
renal portal, or the caudal vein. There is thus a series of segmentally arranged 
commissures between the myelonal vein on the one hand, and one of the sub-vertebral 
series of veins on the other. The commissures receive also feeders from the dorsal 
muscles. 
The subscapular sinus. 
The subscapular sinus (Plate 34, fig. 1 , Plate 36, fig. 16, Plate 37, fig. 21, Subscap. S.) 
is a capacious vessel situated immediately mesiad of the scapula, i.e., between it and 
4 Y 2 
