1002 



HTMAN ANATOMY. 



opposite each constriction (Ranvier). The neurilemma also suffers no break at 



the nodes, but is continuous from one segment to the other. 



In addition to the partial interruptions at the 

 nodes, the medullary sheath after treatment with 

 osmic acid frequently appears broken by clear 

 narrow clefts that extend obliquely from the neuri- 

 lemma to the axolemma and thus subdivide each 

 internodal Moment into a number of smaller 

 known as the S, Iiinidt- I.aiitt -rniann segments 

 ( l-'ig. >44 >. The oblique clefts do not all extend 

 in the same direction, even wkhin the same inter- 

 nodal segment, since they are usually directed from 

 without inward and towards the nodal constrictions 

 and, therefore, have an opposed disposition at the 

 ends of the same a> well as of the adjoining seg- 

 ments. The significance of this subdivision is un- 

 certain ; many regarding the details as artefacts. 

 ding to Capparelli ', however, the apparent 

 clefts are in reality unstained membraneous septa 

 that pass obliquely from the axolemma to the inner 

 suifaee of the neurilc inina and serve to hold the 

 a\i.-.-cylinder in place and to enclose the myelin. 

 The studies of Hatai - on the arrangement of the 

 neurokeratin seem to support these conclusions. 

 Within each internodal segment, beneath the sheath 

 of Schwann, lies a single (sometimes more than 

 one > small nfnrilennna-cell which consists of an 

 elongated oval nucleus surrounded by a meagre 

 amount of cytoplasm. These cells represent the 



remains of the formative elements (sheath-celt's) that during the growth of the 



nerve-fibre were active in providing its envelope (page 101 i 



FIG, 



Node of Ranvier 



Medullated nerve-fibres after treatment 

 with usmif acid; A, fibre showing 

 lutn within medullary coat; . OM showing 

 same coat divided into segments. X 500. 



.itcd nervr ' hi "K 



tin-it li-m;iii..Ui'ii. 



g upon the ])i-esence or absenc- <-f the medullary sheath throughout 



the greater part <>i their course, ner\e tibres are distinguished as medullated or non- 

 1 . \rdiiv f. niikrns. Anat. u. I-'.ntwi.k., M. '>*), [9 



*Joonml of Comparative Neurology, \"i. \iii., i93- 



