loio A MANUAL OF ANATOMY 



left hepatic vein loses its connection with the sinus venosus, and opens into 

 the right hepatic vein at the level where that vein receives the ductus venosus. 

 The common stem, thus formed, is known as the vena hepatica communis, 

 which forms the terminal part of the inferior vena cava. 



The left umbilical vein and the ductus venosus persist throughout foel^l 

 life. Thereafter the ductus venosus atrophies and forms the ligamentum 

 ductus venosi. The left umbilical vein atrophies almost entirely, and gives 

 rise to the round ligament of the liver. A minute portion of its lumen, how- 

 ever, remains pervious at the centre of the round ligament of the liver, and 

 this portion forms an anastomotic channel between the left division of the 

 portal vein and the epigastric veins of the abdominal wall. In this pervious 

 portion the blood can flow towards the umbilicus. 



Anterior Cardinal Veins. — These veins are two in number — right and left — 

 and they return the blood from the head and fore-limbs. Each vein consists 

 of two parts — intracranial and extracranial. The intracranial, part gives 

 rise, directly and indirectly, to the intracranial sinuses, whilst the extra- 

 cranial part, which is the true anterior cardinal vein, becomes the internal 

 jugular vein. The intracranial part is known as the vena capitis medialis. 

 This vein lies at first on the mesial side of the primitive cranial nerve-roots. 

 In this position it is connected with venous loops which embrace the nerve- 

 roots. The mesial portions of these loops disappear, and their lateral por- 

 tions become connected by an anastomotic vessel, which forms another tem- 

 porary vein, known as the vena capitis lateralis. This vein commences just 

 beyond the primitive Gasserian ganglion, and it leaves the cranial cavity 

 in company with the primitive facial nerve, becoming thereafter continuous 

 with the extracranial part of the anterior cardinal vein. 



Vena Capitis Medialis. — This primitive vessel extends as far as the 

 Gasserian ganglion, lying, as stated, on the mesial side of the primitive cranial 

 nerve-roots. The portion of it on the mesial side of the Gasserian ganglion 

 gives rise to the cavernous sinus, and the remainder disappears. 



Vena Capitis Lateralis. — This temporary vein receives three chief intra- 

 cranial tributaries — anterior, middle, and posterior cerebral. The primitive 

 anterior cerebral vein derives its blood from the optic vesicle (eye), fore- brain, 

 and mid-brain. Certain of the tributaries of the anterior cerebral vein, of 

 each side, become connected longitudinally by an anastomotic vessel, lying 

 close to the median line. These two anastomotic vessels, right and left, 

 constitute the rudiment of the superior longitudinal sinus, which sinus is 

 consequently in two halves originally. Subsequently, however, the two 

 anastomotic vessels blend, and so give rise to one superior longitudinal sinus. 

 The primitive middle cerebral vein derives its blood from the cerebellum, and 

 the primitive posterior cerebral vein derives its blood from the medulla oblon- 

 gata. The posterior cerebral vein issues from the cranial cavity through 

 the primitive jugular foramen, prior to joining the vena capitis lateralis, 

 whilst the anterior and middle cerebral veins, having joined the vena capitis 

 lateralis, necessarily issue from the cranial cavity along with the facial nerve 

 through a temporary foramen. 



Subsequently anastomotic connections are formed between the three 

 primitive cerebral veins. The vena capitis lateralis, which, as just stated, 

 leaves the cranial cavity along with the facial nerve, undergoes atrophy, 

 and the venous blood of the entire encephalon issues from the cranial cavity 

 through the jugular foramen. 



Subsequent Metamorphoses. — The superior longitudinal sinus, originally in 

 two halves and developed from certain of the tributaries of the anterior 

 cerebral veins, acquires two anastomotic connections, first with the cephalic 

 end of the middle cerebral vein, and afterwards with the posterior cerebral 

 vein. The latter anastomosis gives rise to the greater or transverse part of 

 the lateral sinus, the posterior cerebral vein forming the sigmoid part of that 

 sinus. The middle cerebral vein becomes the superior petrosal sinus. The 

 inferior petrosal sinus is developed from an anastomotic connection between 

 the dorsal part of the cavernous sinus and the distal part of the lateral sinus. 



