232 Growth and Histogenesis of Nerves 
field’s hematoxylin, followed by Congo-red, dehydrated, cleared, and 
then mounted in balsam. Clearer pictures may thus be obtained in 
early embryos than by the osmic-acid, picro-carmine method used by 
Vignal: 
In a specimen thus prepared (Fig. 1), the bundles of nerve-fibres 
may be seen surrounded by branched, anastomosing mesenchyme-cells. 
Here and there an elongated cell may be seen closely applied to a bundle 
of fibres, but special sheath-cells of this kind are infrequent. In places 
single fibres or small bundles consisting of two or three fibres entirely 
free from sheath-cells may be followed for nearly half a millimeter. 
After teasing the tissue of the spinal ganglion or that from the ventral 
Fie. 1. Portion of the tip of an intercostal nerve isolated from a pig-embryo 8 
mm. long. 720 diam. 
root-zone of the spinal cord, cells may be seen which give rise directly 
to the nervye-fibres, but no cells of this kind are to be found among the 
cells accompanying the bundles of nerve-fibres constituting the nerve- 
trunk. 
As the nerve grows forward new nerve-fibres grow in rapidly from 
behind, and the nerve-fibres as they grow forward give rise to groups 
of fine fibrils. 
The cells found scattered among the nerve-fibres and nerve-fibrils 
multiply actively. As the new cells are formed certain of them give 
rise to a skeletal framework for the support of the nerve-fibrils. The 
periphery of the nerve, also, at an early period becomes covered with a 
fairly complete membrane formed of anastomosing cells. The cells 
within the nerve give rise to branched processes which anastomose with 
