136 
MR. MARSHALL ON THE DEVELOPMENT 
I. DEVELOPMENT OF THE GREAT ANTERIOR VEINS. 
It has been shown by Rathke*, to whom we are chiefly indebted for our know- 
ledge of the development of the veins, that in Man and Mammalia, as in the Verte- 
brata generally, the blood of nearly all parts of the embryo is returned to the heart 
by two pairs of venous trunks, viz. an anterior and a posterior pair, placed symme- 
trically in the lateral halves of the body. Besides these, however, there is a median 
inferior venous trunk, which forms in succession the termination of the omphalo- 
mesenteric and umbilical veins, and finally becomes the vena cava inferior. 
Of the four lateral veins, the anterior pair, formed by branches from the head and 
neck, constitute \\\e, jugular veins. The posterior pair, which return the blood from 
the Wolffian bodies and the hinder part of the embryo, are called the cardinal veins. 
The cardinal and the jugular vein of each side join to form, a short wide vessel, 
named the canal of Cuvier ; and again, the two canals of Cuvier (so named from 
their resemblance to the ductus Cuvieri in fishes) running downwards and forwards 
at the sides of the oesophagus, unite in front of that tube into a common trunk, which 
immediately enters the yet undivided auricular portion of the heart. In the subse- 
quent enlargement of the yet single auricle, this common trunk comes, as it were, to 
form part of that cavity, into which accordingly the two canals of Cuvier henceforth 
open separately, and thus represent two superior venee cavae, one on each side. 
When the Wolffian bodies disappear, the cardinal veins diminish in size, returning 
the blood from the hinder limbs and trunk of the embryo only. In the mean time 
the intercostal veins are formed and united together by vertical anastomoses on each 
side, so as to form the azygos and hemiazygos veins. Finally, in Man, the left 
cardinal vein becomes, according to Rathke, entirehj obliterated, whilst the upper 
portion of the vein of the right side is probably concerned in the formation of the 
termination of the azygos vein. 
In the meantime a transverse connecting branch is developed across the lower part 
of the neck, between the two jugular veins. This transverse branch is rapidly 
enlarged, and then, in the human embryo, and also in those animals which have no 
permanent venous trunk on the left side, that portion of the original left jugular 
trunk which is situated lower down than the transverse branch, or nearer to the heart, 
and also the left canal of Cuvier which is continuous with it, shrink and disappear; 
the enlarging transverse branch across the neck forms the left innominate vein ; and 
the lower part of the right jugular with its canal of Cuvier, receiving the remains 
of the right cardinal vein, now the terminal part of the vena azygos, constitutes the 
vena cava superior as ordinarily met with : thus the metamorphosis is complete. 
In the Sheep, however, it was observed by Rathke, that the upper part of the left 
* Rathke, “ Ueber die fruheste Form und die Entwickelung des Venensystemes beim Scbafe ” (Meckel’s 
Archiv fiir. Anat. und Phys. 18.30, p. 63); also, more particularly, “Ueber den Bau und die Entwickelung 
des Venen.systems der Wirbelthiere ” — (Dritter Bericht, iiber das Naturwissenschaftliche Seminar bei der Uni- 
vcrsitat zu Kdnigsberg. Kdnigsberg, 1838). 
