The finer Anatomy of the Nervous System of Myxine glutinosa. 369 



of W. Müller and Retzius, but he does not seem to have seen the 

 remnant of the S'"^ ventricle described by W. Müller as Trigonum 

 cinereum. 



I have found tliat the ventricles in Myxine are in a different 

 state of reduction in different individuals and in single individuals 

 a nearly complete and communicating system remained. 



Any supposition that the brain should have originally been solid 

 is removed through the researches of Dean (4), Price (32) and 

 KuPFFEK (23). Dean states that the brain of young embryos of 

 Bdellostoma is of distinct tubular structure and differs little in ca- 

 libre from the spinal cord up to a relatively late period in its develop- 

 ment. Price came to the same result with one of his embryos. 



We will now turn our attention to the ventricular system as I 

 have found it in the individuals where it was least reduced. — When 

 the central canal enters the Medulla oblongata from the spinal cord 

 it changes the dumb-bell likeness it possesses in transverse section 

 to a more oval-wedge form. Its dimensions at the posterior end of 

 the Medulla are 112 // in height and 28 f.i in width. On the level 

 of the Vagus nerve it widens a little and its height is then 130 /.i, 

 width 37 i-i. It now becomes gradually larger and more circular; 

 on the level of the Acusticus the height remains the same, but the 

 width has increased to 75 a and it increases in size until the level 

 of the anterior end of the acustic ganglion is reached, w'hen it 

 is 180 ,u high and 90 a broad. There it divides suddenly into 

 two canals, one upper and one lower, both of an oval form and 

 55 jK X 20 fi in size. Both soon become circular in form, the lower 

 one increasing in size and the upper diminishing as the canals con- 

 tinue forwards. The upper one is nearly obliterated, but can be 

 followed into the Tectum opticum, where the canal is once more 

 found wider and it finally enters the rhomboidal cavity of the brain. 

 The lower canal widens gradually, bends somewhat downwards and 

 emerges into the same cavity. All these canals are lined with endo- 

 thelium. Sanders describes a canal without endothelium in the 

 Medulla and which should end in Fossa rliomboidalis. I have not 

 been able to find this cavity in the way it is described by him, but 

 sometimes I have seen in the posterior part of the Medulla oblon- 

 gata, a little above the central canal, a cavity devoid of endothelium. 

 It is doubtful if the cavity Sanders observed in the Medulla and 

 which is devoid of endothelium has anything at all to do with the 

 ventricular system, but may be a bloodvessel which has been widened 



