Primary head veins have been observed in the 10 somite embryo 5074. Corner G.W.(1929) Plate 3
Cardinal veins. In the 14 somite embryo, Carnegie No. 4529, the anterior cardinal is seen at the level of the first somite as an extension of the deep head plexus (termed primitive cephalic vein by Heuser C.H., (1930). It joins the posterior cardinal at the lateral border of the second somite. The posterior cardinal is scantily constructed, in many places lacking a lumen. A strand of angioblasts represents the common cardinal vein. In the 20 somite embryo, Carnegie No. 2053, the anterior cardinal vein is well defined from the cranial border of the 3rd somite (where it joins the posterior cardinal vein to form the common cardinal), to slightly above the 1st somite where it is continuous with the deeper of the head venous plexuses. The posterior cardinal extends continuously to the 5th somite and then caudally to about the twelfth somite in broken segments. The common cardinal vein joins the vitello-umbilical trunk at the level of the 3rd somite. Davis C.L., (1923)
Vitelline and Umbilical veins. In this embryo the vitelline veins (omphalomesenteric) can be distinguished from the vitelline plexus at the level of the eighth intersegmental space. It runs parallel to the aorta, connected with it in various places until it joins the umbilical vein in the septum transversum.
Cardinal veins. The anterior cardinal vein is well defined from where it joins the posterior cardinal vein to form the common cardinal (at approximately the level of somite 5, to slightly above the 1st somite where it is continuous with the deeper of the head plexuses. The description of head plexuses varies so much that no attempt will be made to name veins at this point The posterior cardinal extends from the 5th somite down to about the 23rd somite in a 24 somite embryo. The common cardinal vein joins the vitello-umbilical trunk at the level of the 6th somite Johnson F.P., (1917) Plate 5
Capillaries extending from the sinus venosus towards the lung buds are thought to be the primordia of the pulmonary veins. (Carnegie Embryo No. 5923) cited in O’Rahilly R., Müller F., (1987) p134, fig. 12.8
A large plexus develops in the stroma of the liver. The plexus anastomoses with the vitelline plexus. Large sinus like channels develop bilaterally in the dorsal parts of the plexus and have been referred to as hepatocardiac channels. These drain the liver plexus to the left and right horns of sinus venosus and are the precursors of the post hepatic part of the inferior vena cava. O’Rahilly R., Müller F., (1987) p136
Veins of the head and neck. The anterior cardinal vein drains into the common cardinal vein and is continuous cranially with the primary head vein. At this stage it runs medial to the nerve roots of the vagus (X) and hypoglossal (XII). The primary head vein is medial to the 5th and 10th cranial nerve roots and forms cranially from the merging of the future stem of the anterior dural plexus and the primitive maxillary vein. The capillary plexus of the neural tube drains dorsolaterally into a superficial venous plexus- the dural plexi which are divided into three main regions, the anterior, middle and posterior plexuses, which drain the forebrain/midbrain, cerebellar and medullary regions respectively.
Cardinal and subcardinal veins. The anterior cardinal vein drains into the common cardinal vein and is continuous cranially with the primary head vein. The subcardinal veins begin to develop along the medial side of the mesonephros. They fuse with the posterior cardinal veins at the cranial ends of the mesonephroi and anastomose with the cardinal vein along its length as well as small tributaries from the mesonephric tubules. McClure C.F.W., Butler E.G., (1925)
Umbilical vein. In the region of the liver, the left umbilical vein begins to regress, forming anastomoses with the hepatic sinusoids.
According to McBride R.E., Moore G.W., Hutchins G.M.,(1981), a pulmonary vein is identifiable in 17 out of 25 embryos studied from this stage.
Veins of the head and neck. The primary head vein is well developed with the dural plexuses draining into it via substantial ‘dural stems’ The ventral pharyngeal vein drains the mandibular and hyoid arches into the anterior cardinal although the vein in its first stages is likely to drain into the common cardinal before migrating cranially.
Veins to the limbs. The thoraco-epigastric vein is depicted in a reconstruction of a 5mm embryo designated as belonging to stage 14. It joins the primitive vein of the arm bud before draining into the posterior cardinal. Padget D.H., (1957) The marginal vein is described by Lewis W.H., (1902) in Carnegie Embryo No. 80
Umbilical and vitelline veins. The vitelline veins have formed anastomosis within the liver and around the future duodenal portion of the gut. By the 5mm stage, all umbilical blood passes through the liver sinusoids before passing into the sinus venosus while the vessels connecting the umbilical veins directly to the sinus venosus are no longer patent. By the 6-7mm stage, the right umbilical vein has become attenuated apart from a small portion that will later drain the anterior body wall and most of the placental blood is shunted transversely through the liver to the right hepatocardiac channel which has enlarged with the enlargement of the right sinus venosus. This channel between the left umbilical and right hepatocardiac channel will form the ductus venosus which provides a ‘short cut’ trough the liver for blood returning from the placenta.
Veins of the head and neck. With the descent of the common cardinal vein to the level of the 7th or 8th cervical nerve, the anterior cardinal may now be considered the primitive internal jugular. As the cranial part of the brain is elaborated, so too is the anterior dural plexus. A primitive marginal sinus develops which borders the craniodorsal border of the cerebral hemispheres. Later this vein contributes to the superior sagittal and transverse sinuses. The stem of the posterior dural sinus has migrated caudally to join the head sinus lateral to the tenth nerve root. It later forms the caudal part of the sigmoid sinus. Padget D.H., (1957). Pia arachnoid veins that connect the pial and dural layers of early stages develop. As the neural tube expands and the dural plexuses become further removed from the neural tube, these veins become more conspicuous. At this stage a tributary of the anterior dural plexus is distinguishable and has been named the ventral diencephalic vein. Padget D.H., (1957). Another pia arachnoid vein develops as the primary head sinus deviates lateral to the 10th nerve. It is called the ventral myelencephalic vein and the stem of it later gives rise to the inferior petrosal sinus.
Umbilical and vitelline veins. The are three main anastomoses between the vitelline veins at the caudal end of the liver. Gradually these anastomoses form the portal vein (the cranial most part of the right vitelline) which passes dorsal to the duodenum and branches to give the splenic vein and superior mesenteric vein which course ventral to the duodenum. This rearrangement has, according to Larsen W.J., (1993) pp186-187, occurred by the 35 day stage. In an embryo of this stage described by Barniville H.L., (1915) the vitelline anastomoses around the gut are established and the portal vein anlage is present, connected to the superior mesenteric vein and emptying into the left umbilical in the liver, which continues cranially through the liver as the ductus venosus. Cephalic to the liver the connection between the sinus venosus and vascular plexus in the left lobe of the liver is gradually shifted from the left vitelline vein to the right, thus resulting in a vein leaving the right vitelline vein to supply the left lobe of the liver. This part of the right vitelline vein (between the heart and liver) later becomes part of the inferior vena cava. In the region of the liver, the right umbilical vein has disappeared, bar a small portion that will later drain the anterior body wall. Blood from the placenta is carried to the liver in the left umbilical vein, shunted through the liver via the ductus venosus which connects the left umbilical to the right hepatic channel and into the right sinus venosus. This arrangement is depicted in a reconstruction of Mall’s embryo No 2. (Mall 1906) cited in Keibel F., Mall F.P., (1912) Vol II, Ch. XVIII page 674.
Veins of the limbs. In embryos of this stage a marginal (border) vein has developed around the paddle-like extremity of the upper limb. The lower border of this vein forms the future ulnar vein. This drains, together with the thoraco-epigastric vein into the now called primitive subclavian as its point of drainage has shifted from the posterior cardinal to the anterior cardinal or common cardinal vein Veins are said to pass from the lower limb bud into the posterior cardinal although these are not named. Bardeen C.R., Lewis W.H., (1902)
Veins of the head and neck. According to Padget D.H., (1957)(Fig 7), the primitive straight sinus is distinguishable in Carnegie Embryo No 1121 of this stage.
Veins of the head and neck. A tributary of the primitive maxillary vein is one that runs in the choroidal fissure to the retina. Other tributaries include a medial nasal vein from the olfactory pit and nerve and lateral tributaries from the upper jaw and pterygoid and temporal muscles. Padget D.H., (1957). The linguo-facial vein develops from the ventral pharyngeal vein. It drains into the internal jugular. The telencephalic vein is a tributary of the stem of the anterior dural plexus. It borders the caudoventral margin of the hemisphere and drains the primordial striatal region. Its stem later forms the tentorial sinus while the vein contributes to the superficial middle cerebral veins. There are now several veins distinguishable that traverse the arachnoid layer from the dural plexuses. These include the ventral diencephalic vein, the ventral mesencephalic vein, the ventral metencephalic vein and the ventral myelencephalic vein.
Cardinal and subcardinal veins. There is an extensive anastomosis between the posterior cardinals at their iliac junction. The left posterior cardinal is beginning to regress. McClure C.F.W., Butler E.G., (1925). The subcardinals veins form anastomoses with the posterior cardinals along their length as well as forming an intersubcardinal anastomosis just caudal to the origin of the omphalo-mesenteric (vitelline)artery from the aorta. The right subcardinal has established a connection with the right vitelline vein, while the upper end of the left subcardinal regresses. This results in increased blood return via the right subcardinal and primitive inferior vena cava to the heart. McClure C.F.W., Butler E.G., (1925)
Veins of the head and neck. The jugulo-cephalic vein sprouts from the primitive subclavian vein and may be identified in Carnegie Embryo No 492, of which an ink injected model exists. Padget D.H., (1957)(Fig 6) The thymic/thyroid plexus may also be identified in this embryo.
According to McBride R.E., Moore G.W., Hutchins G.M.,(1981), 5 out of 32 embryos of this stage possessed more than two pulmonary veins.
Cardinal, Supracardinal and Subcardinal veins. A new set of vessels appear during this stage, the supracardinal system. The left and right supracardinals join the posterior cardinals just above the level of the mesonephros and caudally at the level of the iliac anastomosis. The vessels form anastomoses with the posterior cardinals and also an important anastomosis with the subcardinal veins. McClure C.F.W., Butler E.G., (1925)Carnegie embryo no. 841. The posterior cardinals of both sides are beginning to regress while the right subcardinal increases in size.
Veins of the head and neck. The plexiform vertebral vein has formed form the anastomoses between the intersegmental veins and empties into the subclavian or internal jugular. Padget D.H., (1957). The jugulocephalic vein, continuous with the primitive cephalic vein and marginal vein distally and with the internal jugular proximally, arches over the developing clavicle and represents the stem of the future external jugular. Padget D.H., (1957). A plexus develops between the lateral linguo-facial and maxillary vein tributaries., medially a tributary of the maxillary drains a pterygoid plexus. The first definitive sinus has now formed - the sigmoid, dorsal to the otocyst, it is created by an anastomosis between the middle and posterior dural plexuses. The head sinus that is bypassed by this new channel begins to dwindle. Padget D.H., (1957). Continuous with this sinus, between the anterior and middle dural stems is the future transverse sinus. The telencephalic vein continues to grow forming the tentorial sinus- which usually disappears in the human in late foetal stages. Superficial middle cerebral veins drain into it according to Padget D.H., (1957). A plexus is developing in the sagittal plane between the two marginal sinuses. It is the forerunner of the superior sagittal sinus. The stems of the pia arachnoid veins elongate as the dural layer moves away from the neural tube. The choroid plexus of the lateral ventricles drains into the ventral diencephalic vein.
Cardinal, Supracardinal and Subcardinal veins. The posterior cardinal veins degenerate and are incorporated into other venous plexuses except for the caudal plexus which contributes to the distal part of the inferior vena cava. Gasser R.F., (1975) The left common cardinal continues to degenerate such that the developing coronary sinus solely drains the heart. Gasser R.F., (1975). The right part will contribute to the superior vena cava. The cranial part of the right subcardinal dilates to form the suprarenal part of the inferior vena cava, the equivalent left part becomes the left suprarenal. On the left the remains of the intersubcardinal anastomosis becomes the left renal vein and the on both sides the caudal part of the subcardinals becomes the gonadal veins. Gasser R.F., (1975). The caudal part of the right supracardinal does not degenerate and connects the posterior cardinal plexus to the intersubcardinal plexus forming the supracardinal portion of the inferior vena cava. Cranial to this level the supracardinal remains intact on both sides Gasser R.F., (1975). It drains the first ten thoracic intersegmental veins as well as tributaries from the suprarenal. The right supracardinal becomes the azygos and most of the hemiazygos is derived from the left vein. The two are connected by an anastomosis at the lower thoracic levels. Thyng F.W., (1914)
The portal vein forms from the right and left vitelline vein plexus which they form around the future duodenum as it develops. Cranially the veins are continuous with the hepatic sinusoids which have now developed a definite channel (the ductus venosus) which shunts blood through the liver from the left umbilical vein to the hepatic veins which drain into the future inferior vena cava.
Veins of the head and neck. The left brachiocephalic vein has appeared in reconstruction’s of embryos of this stage e.g. Carnegie Embryo No 966 although no explanation as to its appearance is given. Padget D.H., (1957). According to textbook theories e.g. Larsen W.J., (1993), the part of the cardinal vein between the coronary sinus and the internal jugular on the left side degenerates and the left brachiocephalic vein connecting the left internal jugular and subclavian to the superior vena cava, is formed by a new anastomotic channel that develops via the thymic/thyroid plexus. As a venous ring forms around the clavicle, the cephalic vein becomes directly continuous with the subclavian and the jugulocephalic part forms the stem of the external carotid. This vein then anastomoses with the common facial vein during the next few stages. Padget D.H., (1957). The maxillary and linguo-facial veins anastomose and part of the maxillary vein is now considered the deep (common) facial vein Padget D.H., (1957). The tentorial plexus arises from the merging of the anterior and middle dural plexuses. A plexiform superior sagittal sinus has developed from the sagittal plexus between the marginal sinuses. Padget D.H., (1957). Running between the sigmoid sinus and the junction of the tentorial and marginal sinuses, is the primitive transverse sinus. Tributaries drain the choroid plexuses into primitive internal cerebral veins which extend from the straight sinus. Padget D.H., (1957). The ventral myelencephalic vein (future inferior petrosal sinus) is continuous with the remaining small stump of the primary head vein which later develops into the cavernous sinus.
Intraembryonic arterial system
Extraembryonic umbilical veins
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