Franklin P. Mall 17 



If now the vena cerebralis media, as shown in tlie human embryo, is 

 compared with that in TroiDidonotus, and in turn with that of the adult 

 sinuses, it is seen that the vena cerebralis media is the suferior petrosal 

 sinus. They all communicate with the cavernous sinus between the fifth 

 and seventh nerves, they lie lateral to the cranial nerves behind the fifth, 

 and they are also medial to the otic vesicle, i. e., they are within the skull. 

 This latter condition is not yet the case in Fig. 11, but is indicated in 

 Fig. 10, and it is marked by the stub vein near the pons in Fig. 8. 



The dilatation at the posterior end of the superior longitudinal sinus 

 marks the beginning of the torcular Herophili (Fig. 8), and from it the 

 sinus rectus extends towards the choroid plexus, where it ends in the 

 great cerehral vein. Between the straight sinus and the superior sagittal 

 sinus a small vein enters the falx and ends at once in a capillary plexus. 

 This vein no doubt marks the beginning of the inferior sagittal sinus. 

 Behind the transverse sinus (Fig. 8) there is a second venous anastomosis 

 extending from the region of the mid-brain to the internal jugular vein, 

 and no doubt marks the occipital sinus, which in the adult is as an anas- 

 tomosing channel between the upper and lower ends of the transverse 

 sinus. Extending forwards from the juncture of the transverse sinus 

 with the internal jugular vein, a venous sprout is shown in Fig. 8, which 

 passes on the outside of the skull towards the seventh nerve, and marks 

 the remnant of the vena capatis lateralis. 



In the youngest human embr3^os the anterior cardinal veins run on 

 the medial side of all of the cranial nerves before the vena capatis 

 lateralis is formed. In case the whole of the anterior cardinal vein 

 remained permanently, that portion between the cavernous sinus and the 

 internal jugular vein ■\\'ould become the inferior petrosal sinus, for 

 they both hold the same position. But it appears that the inferior pet- 

 rosal sinus is of new formation, for in none of the intermediate stages 

 can a trace of it be found. 



A resume of the development of the sinuses of the brain from the 

 anterior cardinal vein is given in Figs. 14 to 17. They explain them- 

 selves. 



EXPLANATION OF PLATES. 

 Plate I. 



Fig. 1. Surface of the brain with the arteries injected in an embryo 48 

 mm. long (No. 237). Enlarged 5 times; injected by Mr. Brodel. The dorsal 

 end of the cerebral vesicle has been drawn forward to show better the vessels 

 of the mid-brain. 



Fig. 2. Surface view of the brain of an embryo 80 mm. long (No. 234a). 

 Slightly enlarged from a photograph by Dr. Melius. Over the region of the 

 2 



