The Histogenesis of Smooth Muscle in the Alimentary Canal etc. 211 



loped from mesotlielium. He did not trace the later development of 

 the tissue, however. 



Hertz (1869) in a myoma of the uterus, found the smooth muscle 

 arising from small, stellate cells which are separate and distinct 

 elements, with no protoplasmic continuity. The origin of these cells 

 he did not determine. When growth begins, the cells stretch out 

 into spindles and withdraw their processes. The protoplasm, at first 

 distinctly granular, later shows the formation of fibrillae by the granules 

 arranging themselves in longitudinal rows. The fibrillae in every case 

 were found to be very indistinct; but this is easily accounted for, as 

 the work was done entirely upon macerated material. 



Kölliker (1879) in the pig, found that in the oesophagus the 

 muscle first appears close to the cardiac end of the stomach, and that 

 it is the circular layer which develops earliest. 



Müller (1888) in support of the mesothelial theory of His, asserted 

 that in the chick, cells are budded off from the mesothelium of the 

 body cavity, migrate to the aorta, and there form the muscular wall. 



Kölliker (1889) in his „Gewebelehre" summed up the origin of 

 smooth muscle as follows: It proceeds by an elongation of round cells, 

 which, for the most part, are of mesodermal origin, but may be derived 

 also from the ectoderm or endoderm. The mesodermal smooth muscle 

 cells arise in loco in the embryo from ordinary mesenchyme, and in 

 post-embryonic life (as in the gravid uterus) from lymphoid cells. 

 Ectodermal muscle occurs in the glands of the skin and endoderma! 

 in the bronchi of vertebrate embryos. 



Roulé (1891) in vertebrates, held to the mesenchymal origin of 

 smooth muscle. As the mesenchyme is transformed, the stellate cells 

 withdraw their processes and show as rounded granular masses of 

 protoplasm; the cell membranes become very indistinct, if present at 

 all. The muscle cell during growth assumes the form of a spindle, 

 due to the addition of a clear substance, the sarcoplasm, at each end. 

 This finally envelops the original cell but is much more abundant at 

 the two ends of the spindle. The homogeneous sarcoplasm may branch. 

 more or less at the ends, but side branches comparable to intercellular 

 bridges do not form. In the sarcoplasm, the muscle fibrillae appear. 



14* 



