ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 703 



The real function of the hyo-copulo-glossus I believe to be that it acts as the 

 antagonist to the copulo-glossus superficialis. We shall see that the latter muscle 

 evaginates the mucosa anterior to the " tongue " by a ventro-lateral pull on it ; and as 

 the present muscle is also inserted into the ventro-lateral mucosa, it will naturally pull 

 the latter back into the mouth when the " tongue " is withdrawn. It will thus have 

 precisely the same relation to the longitudinalis linguae as the copulo-glossus super- 

 flcialis has to the copulo-glossus profundus. 



16. M. copulo-glossus superficialis. (Figs. 3, 9, c. g. s., c. g. s'., c. g. s".) 



J. Muller, Aussere Vorzieher der Zunge (p. 250). 



Erste „ „ (p. 323). 



,, Oberflcichlicher „ ,, (p. 331). 



A long somewhat powerful muscle, for the greater part of its course closely related 

 to the lateral head of the copulo-glossus profundus. It arises from the dorsal margin 

 of the posterior segment of the basal plate at about the beginning of the taper, i.e. at 

 the posterior end of the anterior third, ventral and somewhat internal to the origin of 

 the copulo-quadratus superficialis, with which it is somewhat closely associated by its 

 dorsal border. In Bdellostoma, according to J. Muller, it arises by two heads from 

 the posterior end of the basal plate. Its posterior half is hidden by the lateral head 

 of the copulo-glossus profundus. Its anterior half comes to the surface between the 

 above two muscles (but is, of course, covered externally by the obliquus), and 

 continues its course downwards and forwards in a slight curve, becoming laterally 

 flattened and fan-shaped as it proceeds. In front it passes abruptly by a wide 

 irregular border a short distance behind the ventral margin of the mouth into a wide, 

 thin, but strong tendon, which fuses completely with that of the other side to form 

 a concave posterior border. This tendon passes straight forwards in the mid-ventral 

 region, and gives off one largish median {c.g.s'.) and a few fine lateral bundles, all of 

 which fuse with the skin immediately behind the ventral margin of the mouth, and in 

 front of the anterior border of the obliquus. The median slip above is also described 

 by J. Muller in Bdellostoma, but P. Furbringer missed it in Myxine. 



The tendon narrows slightly as it approaches the mouth, but on reaching the latter 

 it fans out laterally, and its central portion, after giving off the median slip to the 

 skin above mentioned, bends sharply round the anterior margin of the internal bar of 

 the anterior segment of the basal plate into the mouth, external to the tendon of the 

 copulo-glossus profundus, and begins to pass backwards towards the dental apparatus 

 (this, of course, when the latter is retracted). 



The subsequent fate of the tendon is not only very difficult to ascertain by means 

 of dissections, but this method is actually misleading — at all events as far as preserved 

 material is concerned. I have therefore worked it out in one series of transverse 

 and another of vertical longitudinal sections. However, by splitting the basal plate 



