228 H. S. Harrison, 



cessus partis neglectae is a short dorsal diverticulum giyen off from the 

 ductus as it passes below the pars neglecta (figs. 1, 13). At the point 

 of origin of the recessus, the ductus makes a bend to run directly in- 

 wards to the foramen perilymphaticum, passing through this aperture 

 to join the spatium meningeale (fig. 1). This is of limited extent, pas- 

 sing forwards some little distance in the cranial cavity below the 

 posterior portion of the root of the auditory' nerve, and terminating 

 posteriorly almost immediately behind the foramen perilymphaticum. In 

 Triton it is confined to the ventro-lateral angle of the cavum cranii 

 on each side, and does not extend any great distance either dorsally 

 or towards the middle line. Both Hasse [1] and Retzius [4] state that 

 the ductus perilymphaticus, on entering the cranial cavity, opens into 

 the "cavum epicerebrale". The former observer says, speaking of the 

 frog: "Somit sehen wir denn, dass die Perilymphe einmal durch die 

 Doppelröhre des cavum perilymphaticum und den Saccus perilymphati- 

 cus in ein peripherisches Lymphgefäss und dann, wie bei den übrigen 

 Amphibien, in das cavum epicerebrale abfiiessen kann." In all the 

 Amphibia I have examined, I have tried in vain to detect any free 

 communication hetiveen the restricted perilymphatic system, and any 

 lymj)hatic spaces either ivithin or ivithout the hrain case. The spatium 

 meningeale of Triton is not in communication with the subdural space, 

 as Hasse and Retzius appeared to consider. It lies apparently rather 

 between two layers of the dura mater ^) itself. In this conclusion I 

 am in agreement with Miss O'Neil [8], who gave the term spatium 

 interdurale perilymphaticum to the space in which the spatium me- 

 ningeale lies. It seems probable that Hasse and Retzius, working by 

 means of injection, were deceived by the ease with which the delicate 

 walls of these spaces can be ruptured. 



^) Our knowledge of the cerebral membranes in the lower Vertebrata is still 

 unsatisfactory. For the different views on this question I refer to Gaupp (Anat. 

 des Frosches. Abt. II. Erste Hälfte. II. Auflage) O'Neil [8] and Sterzi [9]. Miss 

 O'Neil's work was done under Prof. Gaupp's supervision. It is clearly a matter 

 of great difficulty to decide how far the disposition of the various layers is de- 

 termined by the ingrowth of structures naturally foreign to the cranial cavity, 

 and how far it is the result of an independent tendency to stratification. The 

 fjuestion is rendered still more difficult by the action of reagents in producing 

 artificial spaces. 



