CONTAINED PERIOTIC TISSUE-SPACES IN THE HUMAN EMBRYO. 15 



more, than a cleft situated between the membranous labyrinth and the bony wall 

 and is traversed by many trabeculae. 



A third author who could be put in this group is Boettcher (1869). He pub- 

 lished two papers which bear upon the periotic spaces, but these are not available to 

 the writer and resort has been had to the account of them given by Retzius (1884). 

 He describes the formation of the scalae in sheep embryos. They make their first 

 appearance in embryos 70 mm. long, beginning in the first turn of the cochlea and 

 gradually extending to the second and third. According to him there is a prelim- 

 inary formation of mucus tissue in the region in which the scalae are to appear; this 

 then undergoes a fatty degeneration, the result being the formation of the spaces. 

 He warns against confusing this special " Schleimgewebe " with ordinary intracap- 

 sular connective tissue and opposes Hensen's theory of its invagination from the 

 outer periosteum. According to him (Boettcher, 1872), it arises in loco out of the 

 original cellular embryonal connective tissue. 



Although it was recognized that there must be a provision in the human adult- 

 ear for the renewal and drainage of the intralabyrinthine fluid, yet there was no 

 positive evidence of how this was accomplished until the introduction of injection 

 methods. Schwalbe (1869) found that when Berlin blue is injected into the sub- 

 dural space the injection mass passes through the internal auditory meatus into the 

 space existing between the bony and membranous labyrinth. Since he could also 

 trace the injection mass from the subdural spaces into the lymph vessels and glands, 

 he therefore believed that the perilymph spaces represented true lymph spaces, for 

 which the arachnoid spaces acted as the main drainage-channels. 



In order to test out the communication reported by Schwalbe between the arach- 

 noidal spaces and the perilymphatic space, a series of injections were made by 

 Weber (1869), who found that the injected fluid accompanied the acoustic nerve as 

 far as the lamina cribrosa, but did not go through this. It passed rapidly, however, 

 through the aquaeductus cochleae into the perilymphatic space of the cochlea. Later, 

 this same investigator (Weber-Liel, 1879) invented the aspiration method by which 

 the results were refined, and he was able to avoid the production of artificial paths 

 which commonly result where strong pressure is necessary for the injection and 

 which apparently had vitiated Schwalbe 's experiments. He proved clearly that 

 the aquaeductus cochleae was the primary path of communication between the peri- 

 lymphatic and arachnoidal spaces, and that it consists of a free canal lined by an 

 extension of dura mater connecting the scala tympani with the cranial cavity. He 

 was not specific, however, as to whether the communication was with the subdural 

 or subarachnoid space. 



Key and Retzius (1875) in their extensive studies on the brain membranes, 

 were able by injection methods to show that the spaces of the brain membranes 

 stood in open communication with the perilymphatic space of the labyrinth, but, 

 although they were able to trace the injection mass along the acoustic nerve, through 

 the lamina cribrosa, and along the finer filaments of the nerve into the lamina 

 spiralis, they were not sure of its communication there with the perilymphatic space. 

 They showed, on the other hand, that the latter could not be injected through the 



