877 ^ 



holds that the „Anlagen" of the cranial, ganglia in the Chick have 

 any connection with the neural plate. Regarding the spinal ganglia 

 his standpoint and that of all other observers, except His, from 

 Balfour and Marshall onwards, is very clear: all maintain that the 

 spinal ganglia are direct outgrowths of the spinal cord. As this 

 point is of extreme importance for the conception of the morphology 

 of the ganglia, both cranial and spinal, which I am about to develop, 

 I will at once assert that they arise totally independently of the neural 

 plate, and that though in some cases there may be appearences such 

 as might be interpreted in the sense of former views, these appear- 

 ances are deceptive, and are to be otherwise explained. For the cra- 

 nial ganglia of the Chick there is, however, no occasion to argue the 

 matter, for in good specimens of Chick embryos between the 22"'^ and 

 28"" hours of incubation, — embryos with from two to ten somites, 

 the epiblastic origin of the cranial ganglia is easily 

 demonstrated. 



In such embryos the neural folds are just meeting, or they have 

 already fused in the head. The thickened epiblast which forms the 

 neural plate passes into a further portion of thickened epiblast along 

 the hne of fusion and external to it dorsally. This as especially the 

 case in the mid brain, but it also holds for all parts of the brain as 

 far back as the „Anlage" of the vagus. 



Looking at sections of an embryo in which the folds are just 

 closing in the mid brain we see that the epiblast beyond and outside 

 he point of closure is composed of several layers of deeply staining 

 cells. And as the closure becomes more complete one may observe 

 an active proliferation of the inner layers of these cells, and finally 

 their separation from the outer epiblast which is left as a single layer 

 of cells. The cells thus separated from the extreme dorsal part of 

 of the epiblast and from the reentering angle of epiblast between this 

 dorsal portion and the neural tube rest on the latter, but are to- 

 tally unconnected with it. 



This process begins in the region of the mid brain, and proceeds 

 backwards as far as the origin of the vagus. The spinal ganglia are 

 formed very much earlier as epiblastic proliferations, but in reality 

 in essentially the same way, of that more later on. 



One may with Marshall call the „Anlage" a „neural ridge" or 

 a neuroganglionic ridge; for from it arise both nerves and ganglia, 

 but I prefer not to give it a special name which may lead to what I 

 conceive are false ideas of it as a morphological entity. For the later 

 segmentation is latently present, and it is only that we can hardly at 



