236 H. S. Harrison, 



metotica^) (foramen jugulare, fig. 27). Through this aperture the re- 

 cessus passes out of the capsule and enlarges to form a considerable 

 perilymphatic space occupying the anterior end of the raetotic fissure, 

 and passing backwards a short distance to end blindly anterior to 

 the points of exit of the ninth and tenth nerves. For the portion of 

 the perilymphatic space lying outside the auditory capsule and the 

 brain case, we may retain the term saceus perilymphaticus , used by 

 several previous observers (fig. 27, 28). The saceus is bounded ven- 

 trally by a membrane continuous with the perichondrium of the outer 

 surface of the chondrocranium. It is not possible to define accurately 

 the respective limits of the recessus partis basilaris and the saceus 

 perilymphaticus, the latter being merely an expanded continuation of 

 the former. 



So far, we have not seen how the recessus partis basilaris is in 

 communication with the ductus perilymphaticus. In Bana fusca this 

 takes place not within the auditory capsule, but within the cavum 

 cranii. As the recessus partis basilaris passes out of the auditory 

 capsule to become the saceus perilymphaticus, it gives off a canal 

 which passes into the cavum cranii through the anterior end of the 

 fissura metotica This is what Gaupp [7] has called the canalis ana- 

 stomoticus (seen in fig. 27) and it appears at once to join the pars 

 meningealis. As a matter of fact I shall give reasons for the view 

 that what is here apparently the posterior part of the spatium me- 

 ningeale, is really a portion of the ductus reuniens, which from a po- 

 sition within the auditory capsule, has been included within the cranial 

 cavity by the alteration in position of the slender bar of cartilage 

 which separates the foramen perilymphaticum from the new aperture 

 in the floor of the capsule (see figs. 18, 19, 20, 26 and 27). 



We ' see then that whereas the ductus perilymphaticus and its 

 aperture into the cranial cavity have much the same relations as in 

 the Urodela, the recessus partis basilaris attains a greater importance, 

 and acquires independent relations with the exterior. For the foramen 

 corresponding to the foramen perilymphaticum of the Urodela, Gaupp [7] 



') This term was introduced by Cianpi) for the cori'espoudii)}^ aperture in 

 Lacerta agilis [14]. 



