8 DEVELOPMENT OF CEREBRO-SPINAL SPACES IN PIG AND IN MAN. 



II. REVIEW OF LITERATURE. 



In order fully to understand the problems which confront one in the study of 

 the embryonic cerebro-spinal spaces, a comprehension of the stage to which investi- 

 gations have brought our knowledge of these fluid-pathways in the adult is neces- 

 sary. It is with this purpose that the adult relationships are here considered. The 

 inclusion of this material may be pardoned, for it will be seen that unanimity of 

 opinion has by no means existed in regard to any of the problems concerned in the 

 circulation of the cerebro-spinal fluid. 



Modern anatomical knowledge of the meninges dates from the work of Axel 

 Key and Gustav Retzius' 29 '. These Swedish investigators, in their excellent mono- 

 graph published in 1875, first conclusively demonstrated the anatomical continuity 

 of the spinal and cerebral subarachnoid spaces. But for years after their publica- 

 tion appeared, a physiological continuity between the subdural and subarachnoid 

 spaces was argued for by many observers, notably by HilU 24 '. Gradually, however, 

 workers in this field have reached the opinion that the subarachnoid spaces (the 

 interrupted but continuous channels between arachnoidea and pia) are functionally 

 the channels for the cerebro-spinal fluid. Between the intra-leptomeningeal and the 

 subdural spaces no anatomical connection exists; physiologically there may be 

 some mode of fluid-passage. Thus Hill 124 ) states that either by filtration or through 

 actual foramina fluid passes readily from one space to the other. Quincke (46) , from 

 observations on animals, somewhat similarly premised a connection between the 

 two spaces, but only in the direction from subdural to subarachnoid. His experi- 

 ments, based on the results of the injection of cinnabar granules, are open to criti- 

 cism as indicating a normal passage-way for the fluid; for, as he has recorded, an 

 intense phagocytosis of practically all of his granules occurred. More modern con- 

 ceptions of the subdural space treat it as a space anatomically closed, lined externally 

 by a polygonal mesothelium. Less error is Introduced if it be regarded as analogous 

 in many respects to well-known serous cavities rather than as an essential portion 

 of the pathway for the cerebro-spinal fluid. 



The question of the absorption or escape of cerebro-spinal fluid from the sub- 

 arachnoid space has claimed the attention of many workers. Since the original 

 conception that the meningeal coverings were actually serous cavities, anatomical 

 investigations have furnished many new views. Key and Retzius, by spinal sub- 

 arachnoid injection of gelatine masses colored with Berlin blue, demonstrated an 

 apparent passage of the injection fluid into the great cerebral venous sinuses through 

 the Pacchionian granulations (die Arachnoidzotten). Their observations were 

 made on a cadaver and the injections carried out under fairly low pressures (about 

 60 mm. of mercury). A lesser drainage of the fluid into the lymphatics was also 

 shown. 



Since the view advanced by Key and Retzius of the absorption of cerebro- 

 spinal fluid, the general trend has been away from the idea of an absorption into the 

 venous sinuses. QuinckeV 46 ) observations, made on lower animals after the sub- 

 arachnoid introduction of cinnabar granules, really offer some substantiation of 



