750 MR FRANK J. COLE 



obliquus fibres crossing over the middle line on to their opposite side, as figured by 

 J. Muller in Myxine. This author, however, erroneously regards these fibres as 

 belonging to the sphincter cloacae. I assume that he is referring to the obliquus, and 

 not to the sphincter, because he says that the fibres arise from the parietalis, and those 

 of the sphincter, of course, do not. Further, the true sphincter is figured behind and 

 distinct from them. On removal of the obliquus the sphincter cloacae is exposed, and 

 the rectum and cloaca may now be removed, with the sphincter intact and in situ. It 

 is a powerful muscle, the origin of which occupied in the above Hag the 7 mm. in front 

 of the cloacal aperture, and commenced just behind the posterior termination of the 

 rectus. There is no question of crossing at the origin. 



The fibres of the sphincter cloacae arise at the mid- ventral line corresponding to the 

 linea of the obliquus, and extend from the ventral wall of the rectum on to the descend- 

 ing ventral wall of the cloaca, but not over the whole of the latter, as above stated. 

 From thence they pass as a compact mass at an obtuse angle backwards, outwards, and 

 upwards in a curve round the lateral wall of the cloaca. Arriving at the dorso-posterior 

 wall or roof of the cloaca, the anterior half of the fibres take a forward bend and pass 

 over into those of the opposite side at right angles to the long axis of the gut, and 

 there is hence (apparently) no mid-dorsal linea here. The fibres forming the posterior 

 half, however, continue their backward course, and hence meet those of the other side 

 at an angle. Consequently there is a mid-dorsal linea here, and there are indications 

 that it is continued forwards throughout the entire extent of the muscle, although it is 

 not obvious in dissection. The anterior three-quarters of the sphincter lie external to 

 the terminal portions of the segmental ducts, so that the muscle will also act as a con- 

 strictor to these. 



35. M. transversus caudalis, F.J.C.* (Fig. 4, t. c.) 

 Schneider, 17, p. 114. 



I had thought that this muscle had hitherto escaped notice, but it is evidently the 

 one briefly mentioned by Schneider. 



The transversus caudalis is a long, irregular, very diffuse and ill-defined muscle, 

 developed to take the place functionally of the obliquus behind the cloaca. It is in 

 fact an extrinsic constrictor muscle of the post-cloacal slime sacks (which, like the 

 others, have no intrinsic musculature), and has no existence apart from them. I include 

 here the two slime sacks generally found opposite the cloacal aperture, since these are 

 morphologically post-cloacal. 



Anteriorly there are a few fasciculi (seven in the present case, fig. 4, obi') which arise 

 like the obliquus, but at a gradually descending level, from the superficial external 

 fascia of the parietalis, and the largest and most anterior bundle is actually serially 

 homologous with the obliquus. These bundles may therefore be said to represent the 



* Described from dissections only. 



