ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 743 



above the neural tube, and a thinning at the side of the neural tube and chorda. In 

 the anterior region of the tail the slime sacks occupy the position of the body cavity, 

 and the parietalis extends externally about half way down on each side of the slime 

 sacks. Such extension must, of course, be purely secondary. Dorsally, the muscle 

 extends above the neural tube at the side of the median dorsal bar, where this exists, 

 whilst behind the slime sacks it stretches below the chorda at the side of the median 

 ventral bar, where it is best developed, and where it coincides with the ventral 

 boundary of the body. It soon begins to thin down, first laterally and then dorsally, 

 and finally terminates in a very small and often irregular myotome on the fused dorsal 

 and ventral bars, slightly behind the posterior end of the spinal cord. 



The function of the parietalis is to effect the sinuous movements by which the 

 animal swims. 



81. M. obliquus, F.J.C. (Figs. 1, 4, 5, 9, 10, obi.) 



J. Mullbb, Schiefe Bauchmuskel (p. 246). 



M. Fdrbringbe, M. obliquus externus (pp. 613 and 628). 



Wiedbesheim, M. obliquus abdominis externus (p. 232). 



I have abbreviated the name of this muscle because it extends not only over the 

 abdominal but also over the respiratory and cranial regions of the body. In a 31 cm. 

 Hag it commenced 7 mm. behind the extremity of the snout as a thin sheet of fibres 

 coursing obliquely in a curve downwards and backwards from the ventral edge of the 

 tentacularis posterior, to which it is attached, and extending along about the middle 

 third of the latter. This anterior more dorsal portion of the muscle entirely or largely 

 covers the small first myotome and the ventral portion of the second (fig. 9). Behind 

 the anterior 6 mm. the dorsal edge of the muscle descends to the more ventral level 

 of the remainder of it, but throughout its whole course covers externally the ventral 

 portions of the myotomes. 



The obliquus is characterised in that portion of it in front of the branchial apertures 

 by an extraordinary interdigitation of its fibres ventrally. On the abdomen the fibres 

 arise as one continuous sheet from the superficial external fascia, but as the latter passes 

 externally to the slime sacks and the obliquus internally to the same, the two are 

 separated for a time. Mid-ventrally the obliquus terminates without overlapping at a 

 ligamentous linea which is connected with tlie superficial fascia, the latter curving 

 upwards and inwards over the median surfaces of the slime sacks to meet it. In front 

 of the abdominal region, however, the fibres of the obliquus, as they approach the mid- 

 ventral line, are first of all collected into definite fasciculi of very variable size, and 

 these terminate, not at a mid-ventral linea, but are continued for some little distance 

 over the median line on to the opposite side of the body to which they belong (fig. 10). 

 The extent of the crossing is greatest immediately behind the mouth, i.e. at the anterior 

 end. From thence it irregularly narrows down to a point at the respiratory apertures, 



