84 SPECIAL HISTOLOGY. 



united upon the sigmoid flexure, into a single longitudinally 

 fibrous layer, which is continued upon the rectum. Beneath these 

 bands there lies a continuous, circularly fibrous layer, thinner 

 than in the small intestines and more especially developed in 

 the duplicatures, which are known under the name of the plicce 

 sigmoidece. 



The rectum possesses a muscular layer of 1'" and more thick, 

 in which the more abundant longitudinal fibres lie external to 

 p . , 2Q1 the circular. The ultimate, somewhat thickened ex- 

 tremity of the circular fibres is the sphincter ani 

 internus, with which the transversely striated sphincter 

 externus and levator ani are conjoined. 



In their elementary structure, all the muscles of 

 the proper alimentary canal belong to the so-called 

 smooth or not-striated (vegetative, organic) muscles 

 (see § 26). Their elements, the fibre-cells, are 

 fusiform, on the average 0002 — 003"' broad, and 

 0-06 — O'l'" long, pale, flattened, and homogeneous, 

 and provided with a nucleus 0006 — 0*012"' long, 

 and 0001 — 0-0028"' broad. 



Many of the fibres present knot-like enlargements 

 and frequently zigzag flexures, which produce 

 the transversely striated appearance of the entire 

 bundles of such muscles so frequently met with in 

 spirit preparations. The arrangement of the fibre- 

 cells in the different strata is simply this ; mutually 

 applied in their length and breadth and cohe- 

 rent, they are united into thin muscular bands, 

 which then, invested with a coating of connective 

 tissue and, frequently, also united into secondary 

 bundles, constitute the thinner or thicker muscular 

 tunics of the different regions ; which, again, are 

 surrounded and separated from the contiguous parts, 

 by considerable layers of connective tissue. 



Blood-vessels are very abundant in the smooth mus- 

 cles; and their capillaries, of 0003 — 0-004'", con- 

 stitute a characteristic 1 network with rectangular meshes. 



Fig. 201. Muscular fibre cell from the small intestine (human). 



1 [Hardly characteristic ; the vessels are arranged in precisely the same way in the 

 fascial aponeuroses; e. g., the fascia lata of the thigh.] — Eds. 



