STRUCTURE OF ORGANIC MUSCULAR TISSUE. 191 



quite parallel to, the margin. This forms the line of demarcation 

 between an external darker and an internal clearer and brighter 

 layer. A similar differentiation of parts may be discerned on 

 examining the transverse section of a fibre in which the cortical 

 layer appears as a dark ring investing the remaining brighter 

 portion. The outer contour of this is always distinctly marked, 

 but its inner is never very sharply defined. The thickness of 

 the cortical layer varies, and in many fibres it is altogether 

 absent. 



Margo* gave a description of certain small points arranged serially 

 in the interior of the fibre cells, and separated from each other by minute 

 intervals ; whilst Wagenerf first described the distinct longitudinal 

 striation that gives the impression of a fibrillar arrangement near the 

 extremities of the fibres. The rows of granules extending from the 

 poles of the nucleus were first mentioned by Klebs,J and subse- 

 quently by Frankenhauser and Wagener.|| 



NUCLEUS. General form and size. The nucleus of the 

 fibre cells is generally single, very rarely multiple, always dis- 

 tinctly rod-shaped, and either rounded at the ends or pointed. 

 It is occasionally curved or spirally convoluted. On transverse 

 section the nucleus appears either round or subangular. It 

 invariably occupies the fusiform enlargement of the fibre, but 

 its position in regard to -the transverse diameter is less 

 constant, since on section it is sometimes seen to lie in the 

 middle of the ring formed by the transverse section of the fibre, 

 and sometimes near the margin. Moreover, the nucleus some- 

 times lies obliquely in relation to the axis of the fibre cell. The 

 length of the nucleus varies from 0*015 0'022 millimeters, and 

 its diameter from 0'002 0*003 millimeters. 



* Neue Untersuchungen iiber die Entwickelung, das Wachsthum und den 

 Ban der Muskelfasern, "Recent Investigations on the Development, Growth, 

 and Structure of Muscular Fibres," 1859. 



f Sitziingsberichte der Gesellschaft zur Beforderung der gesammten 

 Naturwissenscliaften, No. 10, 1859. 



| Virchow's Archiv, Band xxxii., 1865. 



Die Nerven der Gebarmutter und Hire Endigungen in den Glatten Mus- 

 kelfasern, " The Nerves of the Uterus, and their Mode of Termination in 

 fcmooth Muscular Fibres," 1867. 



II Loc. cit. 





