ANATOMY OF A 17.8 MM. HUMAN EMBRYO 83 



Veins 



The general distribution of the veins of the right side of the 

 body is shown in plate 4. Plate 5 is a left lateral, and plate 

 6 a ventral view of part of the anterior cardinal system. 



Anterior and commoyi cardinal system. Between the dorso- 

 medial surfaces of the cerebral hemispheres (plate 4) appears the 

 paired anlage of the superior sagittal sinus {S. sag. sup.). This 

 vessel together with numerous other tributaries arising on the 

 lateral surface of the tel-, di-, and mes-encephalon {Telen.,Dien., 

 and Mesen.) contributes to form the anterior cerebral vein 

 (V.cer.a.) which joins the cephalic end of the cavernous sinus 

 (S.cav.). The ophthalmic vein (V.oph.) which is represented more 

 fully in plate 5, joins the cavernous sinus ventral to the entrance 

 of the anterior cerebral vein. 



Venules arising on the lateral surface of the metencephalon 

 (Meten.) unite to form the middle cerebral vein (V.cer.m.) which 

 passes around the caudal border of the semilunar ganglion 

 •(G.s-l.) to enter the cavernous sinus. 



The cavernous sinus is medial to the semilunar ganglion, and 

 represents a persistent portion of the primitive anterior cardinal 

 vein. The original anterior cardinal from the cavernous sinus to 

 the site of the future jugular foramen, has disappeared, and a 

 temporary vein, the vena capitis lateralis (V.cap.lat.), has formed 

 lateral to the otocyst and the adjacent cranial nerves. The vena 

 capitis lateralis is joined at the caudal aspect of the otocyst by 

 the posterior cerebral vein (V.cer.p.) which takes its origin from 

 a capillary plexus overlying the caudo-lateral surface of the 

 myelencephalon (Myelen.). 



From the point at which it receives the posterior cerebral vein 

 the right anterior cardinal (internal jugular) takes a direct 

 course towards the region of the heart. Dorsal to the heart it 

 unites with the azygos vein (V.az.) to form the right common 

 cardinal (V.card.c.d.). The right common cardinal, which be- 

 comes the proximal part of the adult vena cava superior, empties 

 through the sinus venosus (S.v.) into the right atrium (At.d.). 



