138 Journal of Comparative Neurology. 



A glance at the neural tube of the embryo, represented in 

 plate II of His, zur Geschichte des Gehirns, and the figures 

 6-1 1 of the same work shows us that the cranial part is natural- 

 ly divided into three enlargements, the hind brain ( the part 

 connected with the spinal cord, later called medulla and pons 

 with the cerebellum covering the 'fourth ventricle'), the inid- 

 braiii ( around the aquaeduct of Sylvius) and the forcbrain 

 (around the third ventricle and its projections). Plate II of His 

 gives a good idea of the distribution of the morphological seg- 

 ments of the entire neural stem (brain-stem and spinal cord). 



For an easily comprehensible description of the details of 

 internal structure of this ' neural tube ' composed of spinal cord 

 plus brain, we should give a more fully illustrated resume of the 

 contributions of His. For the present purpose I limit myself, 

 however, to the following sketch of a plan of function and ar- 

 chitecture of the nervous system which we shall use as a work- 

 ing basis for the study of the neurones. Moreover we refer to 

 the summary from His on p. 121. 



The figures 3, 4 and 5 of our plates form our starting 

 point, the former from an early stage of human embryonic life 

 ( His ), giving an idea of the evolution of the various cell-types, 

 the latter from an embryo of Pristiurus (v. Lenhossek ) illustrat- 

 ing the sensory-motor mechanism of one segment. 



In the cross-section of the foetal oblongata ( Fig. 4 ) the 

 cells are found developing into various types ; a certain number 

 remain a simple endothelial lining of the neural canal-ependyma- 

 other cells of a similar type are scattered throughout as cells of 

 the frame-work or neuroglia ; others become more and more 

 highly developed, and form the various types of nerve cells 

 proper. 



(Waldeyer's Mittelzellen) and, to a less extent, the lateral horn cells in the 

 thoracic cord, are arranged in bead-like accumulations but without a relation to 

 the root- segments. An explanation is not offered. The readers of this essay will 

 find that the terms '■segmental ' as used here is usually synonyvions tuith the term 

 'peripheral^ as it is used generally; hut it means spinal peripheral, including the 

 whole of the peripheral neurones and their connections within the neural tube hut 

 with the exclusion of the cerebral and cerebellar mechanisms. 



