VENOUS SINUSES OF THE DURA MATER 



149 



PLEXUS MEDIALIS 



N TRIGEMINUS 



VESICULA AUDITIVA 



V CAPITIS PRIMA 



PLEXUS POST 



Fig. 1 Profile reconstruction of the primary head vein and its tributaries 

 in a human embryo 4 mm. long (No. 588, Carnegie Collection). At the point 

 marked 'A' the vein is bent out of its direct course by the facial and acoustic 

 nerve-mass. The segment included between 'B' and 'C represents the car- 

 dinal portion of the primary head vein, which eventually becomes the internal 

 jugular vein. Enlarged about 33 diameters. 



outlines of the neural tube, the semilunar ganglion and the otic 

 vesicle, are indicated and their relation to the venous system of 

 the head is shown. It happens that this embryo is bent trans- 

 versally in its longitudinal axis, so that its left profile presents 

 a convex surface and its right profile a concave surface. Thus, 



