The Histogenesis of Smooth Muscle in the Alimentary Canal etc. 219 



If this mesenchyme be compared with that surrounding the ventral 

 side of the tube (6) or with the oesophagus in a 7 mm pig (Plate VII, 

 Fig. 1, m) the process of condensation may be observed. The con- 

 densation soon becomes very much more pronounced in the stomach 

 and intestine than in the oesophagus. It is every where brought about 

 by the rapid multiplication by mitosis of the nuclei of the syncytium, 

 with corresponding, increase in the protoplasm. 



In the earliest pig embryo studied, one having a length of 4 mm, 

 the blood capillaries are already present in the mesenchyme, and 

 between this stage and the 8 mm embryo, the nerve cells which later 

 give rise to the plexuses of Auerbach and Meissner appear (Plate VII, 

 Fig. 2, g). The ganglion cells can be distinguished from the mesen- 

 chymal elements, even in the very young embryo, by the more deeply 

 staining qualities of their nuclei (which are abundantly supplied with 

 chromatin), and also by the neurofibrillae in the protoplasm, which 

 stain very intensely with protoplasmic stains (Plate VIII, Figs. 4, 7, 8, 

 ga, gm). Further, the nerve cells group themselves into small ganglia 

 with definite boundaries. 



When the formation of smooth muscle begins in the condensed 

 mesenchyme, it is first of all indicated by a marked elongation of 

 some of the mesenchymal nuclei around the endodermal tube (Plate VII, 

 Fig. 2, mu, Plate VIII, Fig. 4). This nuclear elongation takes place 

 along the entire digestive tract, not in the nuclei immediately beneath 

 the endoderm, but at a distance out in the syncytium. It is so far 

 removed from the basement membrane, that, disregarding other proofs, 

 there can be no doubt of the mesenchymal origin of the muscle. The 

 elongation of the mesenchymal nuclei is, in cross section of the oeso- 

 phagus, seen to be parallel with the basement membrane, so that the 

 tissue assumes an annular, concentric arrangement around the endoderm. 

 The beginning of this can be seen in Fig. 2, which is from the lower 

 oesophagus of an 8 mm pig, but is much better marked in Fig. 3 

 from a 13 mm pig. These annularly arranged nuclei are, of course, 

 those of the circular muscle layer, which, as discovered by Kölliker 

 fl879) appears first. 



The statement that the muscle develops from primitive mesen- 



