244 Caroline McGill, 



Plate XI. 

 (All figures in Plate XI are fi-om sections of adult smooth muscle.) 



Fig. 21. A portion of the circular muscle layer of the adult stomach, showing the 

 persistent syncytium uniting the smooth muscle elements. îïiu = muscle 

 cell; nil = nucleus of muscle cell; ff == fine myofibrillae. (In this 

 particular section there are no coarse myofibrillae.) cf = collagenous 

 fibers; e/ = elastic fiber ; p/> = protoplasmic bridge. Zenker's fluid. Iron- 

 haematoxylin and eosin. x 1425. 



Fig. 22. Smooth muscle from the circular layer of the small intestine of adult 

 pig. In this section the tendency of the fine myofibrillae of the adult to 

 retain the iron-haematoxylin is well shown, cf = condensed reticulum of 

 collagenous fibers; cï = connective tissue cell apparently containing elastic, 

 collagenous, and myofibrillae; el = elastic fiber; nu = spiral muscle 

 nucleus. Gilson's fluid. Iron-haematoxylin and eosin. x 1425. 



Fig. 23. Smooth muscle from the circular layer of the lower oesophagus (adult). 

 //'=fine fibrillae, lying in granular protoplasm; /c = coarse myofibrillae 

 (one breaking up at the end into a brush [br] of fine myofibrillae); c( = 

 connective tissue cell containing collagenous -fibrillae {cf) ; el = elastic 

 fibers. Gilson's fluid. Iron-haematoxylin (no counterstain). x 1425. 



Fig. 24. From the circular muscle layer of the adult large intestine, showing the 

 grouping together of the collagenous fibers into fenestrated membranes 

 {cm). At (tnu) collagenous fibrillae are seen passing for a short distance 

 in among the myofibrillae of the muscle cell. Zenker's fluid. Mallory's 

 anilin-blue connective tissue stain, x 1425. 



Fig. 25. Cross section of adult smooth muscle from the circular layer of the lower 

 oesophagus, showing the collagenous fibers {cf) mostly arranged in rather 

 definite membranes {cm) and the elastic fibers {el) lying either in the 

 membranes or between the membranes and the muscle cells, /f = fine 

 myofibrillae; fc = coarse fibrillae, arranged in some places as „Grenz- 

 fibrillen", in other places as „Binnenfibrillen" scattered throughout the 

 cytoplasm; mw = muscle cell with „ Grenzfib rillen " ; ^ft = protoplasmic 

 bridge; ct = interstitial connective tissue cell. Zenker's fluid. Iron- 

 haematoxylin and eosin. x 1425. 



Fig. 26. From the adult muscularis mucosae of the lower oesophagus, the muscle 

 cells cut in cross section. This shows the immense size of the muscle 

 cells in this region. The large, darkly staining areas {a) are places where 

 the fine myofibrillae are densely grouped around coarse myofibrillae, and 

 from which the haematoxylin was poorly extracted. They represent in 

 places contraction nodes. The coarse myofibrillae show in some places 

 around the periphery of the muscle cells, in other places scattered 

 throughout the protoplasm. In some cells {mu) they are entirely absent. 

 cm = membrane of collagenous fibers; <;/"^ collagenous fibers in a loose 

 reticulum; ff= fine myofibrillae in cross section showing as small pink 

 dots. Gilson's fluid. Iron-haematoxylin and eosin. x 1425. 

 Fig. 27. From the longitudinal muscle layer of the adult large intestine, section 

 parallel to the muscle fibers. This section shows the elastic fibers stained 

 dark blue, the other structures light gray. Zenker's fluid. Weigert's 

 elastic tissue stain, x 1425. 



