BLOOD-VESSELS OF MUSTELUS ANTARCTICUS. 
717 
The brachial vein. 
The brachial vein (Plate 34, figs. 1 and 2, Plate 35, fig. 10, Plate 37, figs. 20 and 21, 
Brack. V.), receiving the blood from the pectoral fin, lies parallel with and imme¬ 
diately mesiad of the metapterygium; at its anterior end it turns inwards, and opens 
into the lateral vein close to its junction with the precaval sinus. 
The iliac vein. 
This (Plate 34, figs. 1 and 3, Plate 37, fig. 24, II. V.) is a short trunk formed by the 
union of the cloacal and femoral veins {infra) ; it receives an anastomotic branch from 
the anterior ventral cutaneous vein (figs. 3 and 14), and opens into the lateral vein 
near the articulation of the basipterygium with the hip-girdle (fig. 24). 
The femoral vein 
(Plate 34, figs. 1 and 3, Fern. V.) lies immediately dorsad of the basipterygium. It 
receives factors from the substance of the fin, and, in the male, from the clasper. 
The cloacal vein 
(Plate 34, figs. 1 and 3, Clo. V.) takes a course nearly parallel to the preceding. It 
receives several large vessels from the cloaca, the anterior of which are also fed by 
factors from the rectum, oviduct, and ovary. Thus the cloacal veins anastomose with 
the mesenteric, spermatic, and oviducal veins. Posteriorly the two cloacal veins 
receive the blood from the posterior ventral cutaneous vein (figs. 3 and 14). 
I think there can be no doubt that the lateral veins, which may now be fairly con¬ 
sidered as characteristic of Plagiostomes, are homogeneous with the epigastric or 
anterior abdominal veins of Amphibians and Reptiles. When first suggesting this 
homology (21) I was unaware of the support afforded to the determination by the 
facts of embryology. In Amphibia (2, p. 539) there are in the embryo two epigastric 
veins which open in front into the sinus venosus, while posteriorly they are connected 
with the iliac veins, and also receive factors from the allantoic bladder and rectum. 
Reference to fig. 1 shows that a very slight shifting of the proximal end of the 
brachial vein would make it open separately into the precaval sinus (anterior vena 
cava), while a displacement mesiad of not more than one or two millimetres would 
cause the lateral vein to open directly into the sinus venosus. 
I have elsewhere (21 and 22) advanced the hypothesis that the lateral vein may be 
looked upon as derived from the vein of the continuous lateral fin of the ancestral 
vertebrate, from which, according to the Balfour-Thacher theory, the limbs of 
vertebrates are evolved. On this hypothesis the discovery of the veins and of their 
relation to those of the pectoral and pelvic fins may be looked upon as an indirect 
