The spiral vein remains as a portion of the original vitelline vein corresponding to the subintestinal segment of the mammalian embryo (cf.
The middle segment of the intestine, presenting a spiral valve in the interior, gives rise to a vein emptying into the portal vein which corresponds to the subintestinal vitelline vein of the mammalian embryo (Fig.
The distal subintestinal segments of the vitelline veins are early united by a transverse anastomotic branch.
The liver, on its development, embraces the subintestinal vein, which then breaks up into a capillary system in the liver, the main part of its blood coming at this period from the yolk-sack.
On this junction being effected retrogressive changes take place in the praeanal section of the original subintestinal vessel.
On the development of the cardinal veins (to be described below) considerable changes are effected in the subintestinal vein.
The portal system is thus established from the subintestinal vein; but is eventually joined by the various visceral, and sometimes by the genital, veins as they become successively developed.
At first a subintestinalvein (vide chapter on Circulation) falls into the lacunae of the yolk-sack, and the blood from these is brought back direct to the heart.
By these changes, and by the disappearance of the postanal section of the gut, the caudal vein is made to appear as a supraintestinal and not, as it really is, a subintestinal vessel.
The arterial trunk is a branch of the dorsal aorta, and the venous trunk originally falls into the heart together with the subintestinal or splanchnic vein.
In the higher Vertebrates the original subintestinal vessel never attains a full development, even in the embryo.
Apart from the non-development of the subintestinal vein the visceral section of the venous system is very similar to that in Fishes.
These considerations, which are supported by numerous other features of their anatomy, such as the character of the axial skeleton, the straightness of the intestinal tube, the presence of a subintestinalvein etc.
On the formation of the liver the proximal end of the subintestinalvein becomes the portal vein, and it is joined just as it enters the liver by the venous trunk from the yolk-sack.
From the dorsal vessel is evolved the aorta (or principal artery), from the ventral vessel the principal orsubintestinal vein.
The other corresponds to the subintestinal vein and the ventral vessel of the worms.
The branches which it gives off to all parts of the body unite again in a larger venous vessel at the underside of the gut, called the subintestinal vein (Figures 1.
The heart is originally only a local spindle-shaped enlargement of the large ventral blood-vessel or principal vein, at the point where the subintestinal passes into the branchial artery, at the limit of the head and trunk (Figures 1.
By these changes and by the disappearance of the postanal section of the gut the caudal vein is made to appear as a superintestinal and not a subintestinal vessel, and as the direct posterior continuation of the cardinal veins.
On this junction being effected retrogressive changes take place in the original subintestinal vessel.
It may be called either the subintestinal or splanchnic vein.
The subintestinal vessel, absent or only represented by the caudal vein and in part by the ductus venosus in higher Vertebrates and adult Fish, forms the main and only posterior venous trunk of Amphioxus and the embryo Scyllium.
The small vessel in it appears to be the remnant of the subintestinal vein.
Embryology proves however that the caudal vein is a true subintestinal vessel[320], and that its connection with the cardinals is entirely secondary.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "subintestinal" in a variety of sentences. We hope that you will now be able to make sentences using this word.
