10 



On the other hand we agree with Holm that the small ventro- 

 lateral root that leaves the bulb in the posterior part of the vagal 

 region and is considered by Sanders to be a vagalroot, is certainly 

 a spino-occipital one (Cf. Holm p. 395), as much on account of its 

 position as on account of its central connection. 



That the spino-occipital column extends for a short distance in 

 the vagal region is a general feature in vertebrates and has been 

 shown before to occur also in Myxine by Edinger ^) (1. c. p. 28). 



We also agree with Holm that the dorsal sensory root entering on 

 this level is a sensory spino-occipital or spinal root and not a sensory 

 Vagusroot, as results from the facts 1. that the size of its fibres 

 corresponds with those of the sensory spinal rootfibres, 2. that the 

 line of entrance and the ascending character of the fibres during 

 their intramedullary course are the same as in the spinal sensory 

 roots and 3. because they are joined by the latter during this 

 course. 



Finally we wish to call attention to the fact that not only the 

 topography of the nuclei, but also the general morphology of this 

 l)rain shows the compression which the brain has suffered. 



Similar to the other ventricles of the brain the 4"^'' ventricle is 

 reduced to a minimum. This is complicated by the peculiarity that 

 the caudal end of the midbrain (a cerebellum does not occur in this 

 animal) protrudes a considerable distance between the dorsolateral 

 walls of the oblongata and is so closely adjacent to it that only the 

 |)ial membrane can follow it. Behind the caudal extremity of the 

 midbrain the dorsolateral walls of the oblongata unite. 



One cannot speak here of a real calamus scriptorius caused by a 

 widening of the ventricle itself. The lateral deviation of the walls 

 takes place only under the influence of the midbrain, but the 4"^'' 

 ventricle itself remains a small split underneath it. The dotted arrow 

 in ligure 2 indicates the place of this pseudo-calamus. Since in this 

 animal, with atrophic eyes, there is no question of an enlargement 

 of the midbrain being the cause of this telescoping, the only reason 

 of it can be found in the compression of the whole brain in its 

 longitudinal axis, which is also exhibited b}' the approach of the 

 vago-occipital part of the oblongata to the trigemi no-facial part. 



This longitudinal compression probably finds its chief reason in 

 the pressure exercised on the frontal part of the l)rain by the 

 olfactory pit and dorsal lip, the influence of which on the form 



1; Edinger : Das Gehirn von Myxine glutinosa. Abhandlungen der Preussischen 

 Akademie der Wiss. 1906. 



