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



spaces around the cranial nerves, especially around the optic pair. Their results, 

 however, are open to criticism, because of the excessive pressures employed ("not 

 over 60 millimeters of mercury") and because the injections were made in fresh 

 cadavers kept warm for periods of 10 or more hours. 



Some of the difficulties concerned in the problems of the perineural spaces were 

 cleared up in a study( 55 ) of the cerebro-spinal circulation published in 1914. In this 

 work injections of true solutions (similar to those used in the present study) were 

 introduced into the spinal subarachnoid space in living cats and dogs, under pressures 

 but slightly exceeding the normal intraspinal tension. These injections were con- 

 tinued for several hours, and the course of the injection fluid was then established 

 by precipitating the solution in situ. By means of this procedure, which it was 

 believed approached the physiological, the perineural spaces around the cranial 

 nerves could be demonstrated. In these adult laboratory mammals the cerebral 

 nerves without exception showed prussian-blue granules in a perineural relation, 

 extending outward along the nerves beyond the termination of the dural cuff. This 

 extension of the injection mass outward was more striking around the first two cranial 

 nerves than about any of the others. Thus, the olfactory nerves uniformly showed 

 perineural deposits beyond the cribriform plate, extending downwards into the 

 nasal epithelium, while the optic nerves were surrounded by the granules in the 

 infravaginal sheath, which spreads out over the posterior surface of the eyeball. The 

 caudal cranial nerves were likewise characterized by extensive perineural injections. 



These findings were interpreted as evidencing a true perineural space, probably 

 of only capillary thickness, which could be injected by filling the cerebro-spinal 

 spaces with a demonstrable true solution. As far as could be made out under the 

 microscope, they had no appreciable existence except when filled with the precipi- 

 tated true solution. These spaces were not filled in the early moments of the injec- 

 tions under low pressures, and could be demonstrated only when the injection had 

 been continued for several hours. 



The perineural spaces are quite different from the spaces surrounding the spinal 

 ganglia and the ganglia of the cranial nerves. These ganglia lie in the true sub- 

 arachnoid space, with the dura investing the arachnoid membrane. Distal to the 

 ganglion the dura ends upon each nerve. In the injection under low pressure with the 

 ferrocyanide the cranial and spinal ganglia were all surrounded by the precipitated 

 salts; the cranial nerves showed extensive perineural injections, whereas the spinal 

 nerves rarely showed a true perineural injection, and then only of limited extent. 



The existence of perineural spaces in the embryo, however, has been under 

 dispute. The larger nerves in sectioned embryos almost invariably show spaces 

 about them, either a complete separation of the surrounding mesenchyme or a 

 partial dilatation of the mesenchymal interstices. Sabin^ 49 ), in 1902, noted that hi 

 perispinal injections with india ink the spinal nerves could be outlined by the carbon 

 granules, but in no case did such an injection run into true lymphatic channels. 

 No evidence was afforded by her work of any lymphatic channels arising from these 

 apparent perineural channels. 



