368 John F. Holm 



The ventricular system. 



The remnants of this system are of very insignificant dimensions ; 

 I have found that they vary considerably in the different individuals 

 of Myxine and it is easy to understand that earlier investigators 

 doubted the existence of any ventricular system at all; Anders 

 Retzius (36) considered the brain of Myxine to be entirely devoid 

 of anything of the kind; Johannes Müller (27) believed that beyond 

 the sinus rhomboidalis and the cavity situated between the upper 

 and inner fasciculi of the Pedunculi cerebri no cavities were to be 

 found; Wilhelm Müller (28, 29) states that the anterior part "of the 

 Thalamencephalon contains the remains of the rostral part of the 

 S""*^ ventricle and which according to its position relatively to the 

 optic nerve ought to be homologous with the Trigonum cinereum. 

 This cavity should extend upwards and by an archiform canal com- 

 municate with the Infundibulum. In his other publication we get 

 some additional knowledge on the subject; he found 0,5 mm below 

 the surface of the Mesencephalon a 0,03 mm wide cavity which com- 

 municated in caudal direction with the sinus rhomboidalis, ending 

 rostrall}' blind in the middle of the Mesencephalon and having all 

 along a coating of cylindrical epithelium. From the end of this 

 cavity he could follow a fine line studded with cell nuclei and he 

 supposed that they indicated the direction in which the ventricles 

 had gone. A fissure opens one millimeter below this point and 

 widens towards the base of the brain. 



The infundibular cavity shows a triangular form both in trans- 

 verse and sagittal sections. 



Gr. Retzius (38) describes the ventricular system in the same 

 way as W. Müller, but he found the foremost remnant of the 3'^'^ ven- 

 tricle isolated. He says: »On sagittal sections of the Myxine brain 

 one meets in the anterior and ventral region a small medially situated, 

 isolated cavity, which perhaps is identical with the formation 

 W. Müller describes and calls Trigonum cinereum. 



This cavity is probably a remnant of the 3^^'^ ventricle. He 

 finds (39) the glanular part of the infundibular process always sepa- 

 rated from the rest by a thin lamin of connective tissue and con- 

 siders this glanular part alone homologous to the hypophysis. From 

 the infundibular cavity he finds two canals that run laterally on each 

 side into the base of the brain. 



Sanders (41) description agrees on the main points with those 



