1907,] ANATOMY OF CHLAMYDOSELACHUS. 473 



the others. A wide and veiy distensible cesophagus follows, and 

 this passes without any external mark of differentiation into the 

 stomach. This organ is U-shaped, one arm being much longer than 

 the other, which is, at first sight, scarcely noticeable. The longer 

 arm of the stomach (text-fig. 138, S) ends in a small caecum (0). 

 Opposite the caecum, the stomach-wall is thickened, perhaps by a 

 lymphatic gland (L.T.S.). This thickening, on account of its 

 position, would probably function as a valve between the two arms 

 of the stomach. The walls of the stomach are irregularly corru- 

 gated. The shorter arm of the stomach (S') differs from the larger 

 anatomically and functionally. It is a .short, thick-walled tube 

 incapable of distension, the lining mucosa of which is raised into 

 parallel ridges. This arm opens into the intestine by a protruding 

 pyloric aperture (Py. V.) which is furnished with distinct sphincter 

 muscles. The relatively narrow lumen of the shorter arm of the 

 stomach, combined with the action of the pyloric sphincter, acts as 

 an efiicient guard against the passage of large pieces of partly 

 digested food into the colon. Anything but a semi-liquid chyle 

 might produce a serious obstruction in the course of the long and 

 complicated spiral valve. 



The bile-duct (B.D), which traverses the anterior division of 

 the spleen, becomes joined to the anterior part of the " bursa 

 entiana " (B.E). It then rapidly enlai'ges, and finally opens into 

 the bursa by an aperture the diameter of which equals the semi- 

 diameter of the latter. The terminal third of the duct has its lining 

 mucosa raised into parallel striae which are continuous with those 

 seen in the first part of the colon. This suggests that the region 

 which appeal's to be the terminal portion of the bile-duct is, in 

 reality, an evagination of the colon towards the bile-duct. Owing 

 to the presence of the striae, the bile must pass backwards towards 

 the spiral valve and not forwards into the bursa entiana. The 

 bursa, which is a thin-walled sac, may serve as a distensible 

 receptacle for the partly digested food before it is passed on in small 

 quantities into the comparatively inelastic colon. The pancreatic 

 duct opens into the region where the spiral valve begins ; hence, 

 although gastric digestion may continue in the bursa, intestinal 

 digestion cannot begin until the food reaches the spiral valve. 

 The so-called colon has thick walls. Its shape is that of a double 

 cone, the widest part varying in position, but in both of my speci- 

 mens it was near the region of the contorted coil. The widest part 

 has the thickest walls. In the specimen examined the spiral valve 

 had 43 coils (text-fig. 138). The valve at the very beginning is a 

 well developed ridge, but at the end it tails off gradually. In the 

 specimen figured by GUnther (2) there were only 35 turns, whilst 

 the valve both began and ended gradually. In both Giinther's 

 specimen and that under discussion, the anterior cone-like coils 

 pass forwai'ds, the postei-ior backwards. Both specimens have an 

 intei-mediate region of one coil in which the valve is contorted. 

 Of the 35 coils in Giinther's specimen 19 pass forward, one is 

 contorted, and 15 pass backwards ; of the 43 coils in my specimen 



