522 ANGIOLOGY 





of the right subcardinal vein, the postrenal part of the right cardinal vein, and the 

 cross branch which joins these two veins. The left subcardinal disappears, except 

 the part immediately in front of the renal vein, which is retained as the left supra- 

 renal vein. The spermatic .(or ovarian) vein opens into the postrenal part of 

 the corresponding cardinal vein. This portion of the right cardinal, as already 

 explained, forms the lower part of the inferior vena cava, so that the right spermatic 

 opens directly into that vessel. The postrenal segment of the left cardinal dis- 

 appears, with the exception of the portion between the spermatic and renal vein, 

 which is retained as the terminal part of the left spermatic vein. 



In consequence of the atrophy of the Wolffian bodies the cardinal veins diminish 

 in size; the primitive jugular veins, on the other hand, become enlarged, owing to 

 the rapid development of the head and brain. They are further augmented by 

 receiving the veins (siibclavian] from the upper extremities, and so come to form 

 the chief veins of the Cuvierian ducts; these ducts gradually assume an almost 

 vertical position in consequence of the descent of the heart into the thorax. The 

 right and left Cuvierian ducts are originally of the same diameter, and are frequently 

 termed the right and left superior venae cavae. By the development of a transverse 

 branch, the left innominate vein between the two primitive jugular veins, the 

 blood is carried across from the left to the right primitive jugular (Figs. 479, 480). 

 The portion of the right primitive jugular vein between the left innominate and 

 the azygos vein forms the upper part of the superior vena cava of the adult; the 

 lower part of this vessel, i. e., below the entrance of the azygos vein, is formed by 

 the right Cuvierian duct. Below the origin of the transverse branch the left 

 primitive jugular vein and left Cuvierian duct atrophy, the former constituting 

 the upper part of the highest left intercostal vein, while the latter is represented 

 by the ligament of the left vena cava, vestigial fold of Marshall, and the oblique 

 vein of the left atrium, oblique vein of Marshall (Fig. 480). Both right and left 

 superior venae cava3 are present in some animals, and are occasionally found in the 

 adult human being. The oblique vein of the left atrium passes downward across 

 the back of the left atrium to open into the coronary sinus, which, as already 

 indicated, represents the persistent left horn of the sinus venosus. 



Venous Sinuses of the Dura Mater. 1 The primary arrangement for drainage of 

 the capillaries of the head (Figs. 481, 488) consists of a primary head vein which 

 starts in the region of the midbrain and runs caudalward along the side of the 

 brain tube to terminate at the duct of Cuvier. The primary head vein drains 

 three plexuses of capillaries : the anterior dural plexus, the middle dural plexus and 

 the posterior dural plexus. The growth of the cartilaginous capsule of the ear and 

 the growth and alteration in form of the brain bring about changes in this primary 

 arrangement (Figs. 483-488). Owing to the growth of the otic capsule and middle 

 ear the course of the primary head vein becomes unfavorable and a segment of it 

 becomes obliterated. To make the necessary adjustment an anastomosis is estab- 

 lished above the otic capsule (Fig. 483) and the middle plexus drains into the poste- 

 rior plexus. Then the anteror plexus fuses with the middle plexus (Fig. 484) and 

 drains through it and the newly estabished channel, dorsal to the otic capsule. 

 All that remains of the primary head vein is the cardinal portion or internal jugular 

 and the part in the region of the trigeminal nerve which may be called the cavernous 

 .sinus. Into it drain the orbital veins. The drainage from the cavernous sinus is 

 now upward through the original trunk of the middle plexus, which is now the 

 superior petrosal sinus, into the newly established dorsal channel. This dorsal 

 channel is the transverse sinus (Figs. 485-488). The inferior petrosal sinus appears 

 later (Fig. 486) . From the anterior plexus a sagittal plexus extends forward from 

 which develops the superior sagittal sinus (Figs. 484-488). The straight sinus is 



Streetcr, Am. Jour. Anat., 1915, vol. xviii. 



