Chapter 3 (page 13)

The Pyloric Sphincteric Cylinder in Health and Disease

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Chapter 3 (page 13)

The longitudinal muscle formed a continuous layer over the pyloric aperture in all of the specimens from subjects aged more than one year. In the average subject from 21 to 24 percent of the longitudinal fibres of the pyloric region, consisting of the more superficial bundles, were continuous with those of the duodenum. Most of the deeper longitudinal fibres, as they approached the pyloric "sphincter", dipped into the circular coat to take part in the formation of the "sphincter", some reaching the submucosa. From the anatomical arrangement it was concluded that these longitudinal fibres constituted the dilator muscle of the pylorus. (Comment: The term "sphincter" apparently indicated the pyloric ring).

In the microscopic sections some variations were found, depending mainly on the point on the circumference at which biopsies were taken. These variations did not appear to follow a definite pattern; in one specimen for instance, there were small areas on the anterior surface of the duodenum where both circular and longitudinal fibres were absent. In l9 percent of the sections, not only the circular, but also the longitudinal coat showed a break at the pylorus. Occasionally a few circular fibres from the pyloric ring were seen to be continuous with the circular fibres of the duodenum.

Cole (l928) did not describe his anatomical dissections in detail but came to the conclusion that the distal part of the gastric "antrum" was surrounded by a dense, thick, fan- or harp-shaped muscle. It seemed to fan out from a narrow area on the lesser curvature to a relatively wide area on the greater curvature (Fig. 3.4). It was apparently a continuation of the circular muscle coat, but its size and density suggested that it was a special division with a specialized function. When contracting, it did so in a segmental or concentric, rather than peristaltic way; full contraction of this muscular structure caused the formation of the pyloric canal (not to be confused with the pyloric aperture). Normally the fan-shaped muscle contracted during a short stage of each gastric peristaltic cycle; it was also contracted during rigor mortis. (Comment: The "fan-shaped" muscle described by Cole corresponds to Cunningham's sphincteric cylinder and Forssell's canalis egestorius).

Fig. 3.4. F.M., fan-shaped muscle according to Cole; its concentric contraction causes formation of the pyloric canal; P.A., pyloric aperture

Torgersen (l942) studied the muscular build and movements of the stomach and duodenal bulb from the point of view of comparative anatomy and embryology. Although his methodology was quite different from that of Forssell (1913), his results verified the latter's conception of the canalis egestorius in all important respects and he accepted Forssell's terminology. He differed from Forssell in a few details; for instance, whereas Forssell included part of the membrana angularis on the lesser curvature in the canalis egestorius, Torgersen regarded these as two separate regions.

Torgersen (l942) was able to add important new findings which further elucidated the muscular anatomy of the "transverse" part of the stomach. His monumental work commenced with an historical review of the anatomy of the stomach from the time of Willis (1682) to the era following Forssell (1913). He showed in detail how previous anatomists such as Retzius, Luschka, von Aufschnaiter, Jonnesco and E. Müller opened the way for Cunningham (l906) and Forssell (l913). On the other hand a few anatomists, the most notable being Pernkopf (l922, l924), differed from the latter; while Forssell held that the musculature of the stomach was highly differentiated into separate but contiguous regions, Pernkopf maintained that there was no differentiation in the musculature at all. According to Pernkopf the regions lacked anatomical foundation, and the forms of movement were entirely of a functional nature; nevertheless he agreed that the movements were not devoid of comparative anatomical interest, as they imitated the more complex stomachs of other vertebrates.

According to Torgersen (l942) the circular musculature of the canalis egestorius in man and other vertebrates contains two annular thickenings or loops. The aboral loop is called the right canalis loop (Fig. 3.5). (Comment: At times he also referred to this loop as the pyloric sphincter; the word "sphincter" was an unfortunate choice, as it will become clear that Torgersen regarded the "sphincter" as a complex structure consisting of various loops, of which the right canalis loop constituted but one component. In a personal communication to the present author in 1962, Torgersen confirmed that the right canalis loop was the muscular component of the pyloric ring).

Fig. 3.5. Diagram of circular musculature of sphincteric cylinder (canalis egestorius) according to Torgersen. R.P.L., right pyloric (canalis) loop; L.P.L., left pyloric (canalis) loop; P.M.K., pyloric muscle knot (torus); S, stomach; D.B., duodenal bulb. (Ring of circular musculature surrounding commencement of duodenum not shown.)