ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 735 



J. Muller's description of Bdellostoma, where this loop has precisely the same 

 relations as most of the others. In this region and that of the ventral insertion Muller 

 figures and describes in Myxine a very obvious and elaborate decussation of the fibres 

 round the gut, both dorsally and ventrally, but the description is by no means clear 

 (and indeed he recognises this himself), and the figures are too small and vague to be 

 of much assistance. It is improbable that Muller was mistaken in his facts ; and as 

 I have never seen any decussation of fibres except the slight one mentioned above, 

 this can only be regarded as another of those extreme variations which this perplexing 

 muscle exhibits. [Since this was written, however, I have found a distinct ventral 

 decussation in one of my series of sections. The paired tracts forming the inner 

 portions of the ventral insertion, after passing backwards under the gut, fused first 

 with each other and then with the cardiac portion of the constrictor in such a way that 

 each tract sent fibres both to its own and to the other side of the gut.] 



Ventral Insertion. — We are now in a position to describe the ventral insertion of 

 a large number of the fibres of the branchial portion of the constrictor. On each side 

 a fan-like tract collects in front of the external branchial aperture (figs. 2, 3, 13, 8, 8') 

 and passes between the two recti muscles, to be inserted into the internal fascia of the 

 obliquus at the mid-ventral line. I have seen in some cases a few slips inserted into 

 the internal fascia of the rectus itself, but generally the latter muscles may be entirely 

 removed without in any way interfering with the insertion. J. Muller describes the 

 fibres as inserted into the rectus muscle on each side of the middle line. Apart from 

 the few slips mentioned above, I have never seen this, either in dissections or sections 

 [but cp. the description given below of the sixth loop in the sections], and should have 

 concluded it to be an error on Muller's part, were it not for the extensive variation 

 characteristic of the constrictor generally. The insertion consists of an outer and an 

 inner portion on the left side, made up from the following sources : — 



1. Outer Portion (figs. 2, 3, 13, 8'). — The last or sixth loop (6) forms the greater 

 part of this section, but a tract is usually contributed by the fibres that curve round the 

 internal surface of the ductus oesophago-cutaneus from behind (cp. fig. 3), and also a 

 few longitudinal fibres reach it straight from their origin on the ventral surface of the 

 cardiac portion of the constrictor at the side of the origin of the ventral longitudinal 

 tract. 



2. Inner Portion (figs. 2, 3, 13, 8). — This is not invariably separate from the outer 

 portion, but always more or less so. It consists of a large number of fibres which 

 curve round the ductus oesophago-cutaneus as above described, of many which pass 

 straight on to it from the ventral surface of the cardiac portion of the constrictor, and 

 of fibres from the loops 4 and 5. These loops may be entirely connected with the 

 inner portion of the insertion (as in fig. 13, and, as I believe, is more frequently the 

 case), or they may be more or less connected with the ventral longitudinal tract. In 

 any case, however, all their fibres do not pass into the ventral insertion, or forwards 

 into the ventral longitudinal tract, or both, but a varying number curve backwards 



