416 Transactions. — Zoology. 



small veins (hce) from the cloaca and rectum. These latter, I have no doubt, 

 although I have not actually proved it, anastomose with factors of the portal 

 vein. 



It is by no means easy to find a correct nomenclature for this vein, as 

 it differs so markedly from anything hitherto known. The part between the 

 entrance of the femoral vein and the cardinal sinus (il. h) seems to corre- 

 spond in all essential respects to the iliac vein ; or, as it also receives the 

 hoemorrhoidal veins [hce] from the rectum and cloaca, it may perhaps be best 

 called the ilio-hcemorroidal vein. The part continued forwards, from the 

 junction of the femoral (ejj.g) receives veins (ab.) from the abdominal walls, 

 and therefore answers functionally as well as topographically to the epi- 

 gastric or anterior abdominal vein. Similarly, the anterior part (m) — that 

 continuous with the brachial vein, seems to answer to the mammary vein 

 of the higher animals. So that it may be said, that the mammary and 

 epigastric veins are of great size, as large in fact as the subclavian and 

 iliac, into which they respectively pour their blood, and that they are 

 continuous with one another, instead of merely anastomosing. 



But it is obvious that there is another and more natural way of describ- 

 ing these vessels, namely, by considering the veins I have called brachial, 

 mammary, epigastric, and ilio- hoemorrhoidal, as forming — as they actually 

 do — one continuous lateral trunk, into which debouche the veins from the 

 fore and hind limbs and abdominal walls, as well as from the rectum and 

 cloaca. 



Certain theoretical considerations invest this mode of interpretation with 

 great interest. The theory of vertebrate limbs, now very generally received, 

 is that of Mr. Balfour, who regards the limbs as being detached portions 

 of an originally continuous lateral fin. 



It seems to me that an argument distinctly in favour of this theory, is 

 afforded by the case now under consideration. The ancestral vertebrate 

 possessing the continuous lateral fin must presumably have had a large 

 lateral vein, into which opened numerous veinlets from the fin, and it is 

 reasonable to suppose that, as certain portions of the fin developed at the 

 expense of the rest, the anterior and posterior ends of the vein, in relation 

 with them, would take on a greatly increased size, the intermediate part 

 becoming proportionately reduced, and supplying finally, only the body- 

 wall between the fore and liind-limbs. 



According to Professor St. George Mivart, the skate presents us with a 

 nearer approach than any known type, to the primitive form of limb- 

 skeleton — the archipterygium. If this view be correct it is very interesting 

 to find the limb possessing what we may consider as an almost primitive 

 venous supply. But it must be remembered that, the skate being in many 



