VII. Explanation of Plates. 



Abbi'eviations. 



b = basement membrane. {/a ■■ 



br = brush of fine myofibrillae. gm ■■ 



cf = collagenous fibrillae. gp 



cm = collagenous membranes. gs ■■ 

 ct = connective tissue cell (embryonal 



or adult). hs 



cp = blood capillary. tn ■■ 



e = endodermal epithelium. mes ■■ 

 ecs = embryonal connective tissue syn- mm ■■ 



cytium. mt 



el = elastic fibers. mu 



fc = coarse myofibrilla. nu 



ff = fine myofibrillae. pb ■■ 



g = ganglion cell. vf 



ganglion cells of Auerbach's plexus. 



ganglion cells of Meissner's plexus. 



granular protoplasm. 



granular spindle (anläge of coarse 



myofibrilla). 



homogeneous spindle. 



mesenchymal syncytium. 



mesotheUum. 



muscularis mucosae. 



mitosis. 



muscle cell. 



nucleus of muscle cell. 



protoplasmic bridge. 



varicose myofibrilla. 



Plate VII. 



Fig. 1. Portion of a cross section of the lower oesophagus of a 7 mm pig, showing 

 the condensed mesenchymal syncytium (m), continuous with the mesothelial 

 cells (mes) , but separated from the endoderm (e) , by the basement mem- 

 brane (b). The reticular structure of the granular cell protoplasm shows 

 clearly, mt = mitosis in the endoderm , the long axis of the spindle 

 parallel with the basement membrane, cp = blood capillary containing 

 nucleated blood corpuscles. In this stage, the elongation of the mesen- 

 chymal cells to form smooth muscle has not yet begun. Zenker's fluid. 

 Alum-cochineal and Congo-red. x 1045. 



Fig. 2. Portion of a cross section of the lower oesophagus of an 8 mm pig, 

 showing the beginning elongation of the condensed mesenchyme cells (m), 

 to form muscle cells (mu). The elongation begins at a distance from the 

 basement membrane {h); e = endodermal epithelium; mt = mitosis in an 

 endoderm cell; ^ == sympathetic ganglion cells; jt?& := protoplasmic bridges 

 helping to form the syncytium. Fixation, Zenker's fluid. Stain, alum- 

 cochineal and Congo-red. 



