12 Development of Blood- Vessels of ITuman Brain 



cnniarkos an. Dabci gclit die Balm durch das Foramen jugulare 

 entweder vollstandig oder zum Theil zii Grunde. Die bei den meisten 

 Saiigern auftretendc sekundare Yerbindung ist die, welche das Foramen 

 jugulare spurium zum Austritte benutzt, doch giebt es auch Thier- 

 formen, z. B. die Ivatze, bei denen ein solclies gar nicht zur Ausbildung 

 kommt, obwohl die Vena jugularis interna fast vollstandig zu Grunde 

 gegangen ist. Hier treten eben die sekundaren Verbindungen, welche 

 die Orbital- und Nachhirnvenen eingehen, fiir diese Gefasze ein. Mithin 

 kann man Avohl behaupten, dass die Vena jugularis interna als Fort- 

 setzung des Sinus transversus, wie sie beim Mensclien und beim Aflen 

 am schonsten ausgebildet ist, ein primitiveres Verhalten darstellt, bei 

 ■\v-elchen die Vena jugularis externa die hauptsachliclie, wenn nicht die 

 einzige abfiihrende Bahn des Schiidelinneren darstellt. 



It is apparent from the above that the beginning of the internal 

 jugular vein is marked by the twelfth nerve crossing the anterior cardinal 

 vein and that it extends to the lateral sinus through a number of 

 sprouts behind the otic vesicle (Fig. 13). The vena capatis lateralis 

 is that portion of the anterior cardinal vein which wanders to the lateral 

 side of the cranial nerves and extends from the twelfth to the fifth nerve. 

 The portion of the anterior cardinal vein which lies medial to tlie fifth 

 nerve retains that position throughout its development and marks the 

 cavernous sinus (Fig. 10). Into the embryonic cavernous sinus there 

 empties the ophthalmic and anterior cerebral veins. The latter soon 

 extend to the embryonic superior sagittal sinus. Between the fifth 

 and 7th nerves a vein extends to the region of the cerebellum, the vena 

 cerebralis media (Figs. 9, 10 and 13), and behind the otic vesicle there 

 extends through the embryonic jugular foramen the vena cerebralis 

 posterior (also shoAvn in Fig. 11). 



We have, therefore, in the embryos of the second month an arrange- 

 ment of the veins in tlie head similar to that found in the reptiles as 

 shown by Groszer and Brezina,'' and I shall employ the nomenclature 

 of these authors. The anterior cardinal vein shifts lateralwards and 

 by the end of the first month is partly lateral to the otic vesicle as sliown 

 in Fig. 3. The process is shown more advanced in Fig. 9, and is com- 

 plete in Fig. 13. The condition shown in Fig. 13 is that which is per- 

 manent in selachians. Now the reptilian stage is entered. From the 

 lateral vein — the vena capatis lateralis — three veins extend into the 

 head and encircle the brain. The first — the vena cerebralis anterior 

 (shown well in Fig. 10) — passes up and over the cerebral vesicle, i. e., 



'== Groszer and Brezina: Morph. Jahrb., XXIII, 1895. 



