ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 705 



greater, part of the tendon, it follows that one important function of the copulo-glossus 

 superficialis is to exercise a forward pull on the teeth themselves. Similarly, the other 

 important function of the muscle is to evaginate the antero- ventral mucosa of the mouth. 



The lateral slip may be traced forwards in the longitudinal sections up to a short 

 distance behind the base of the cartilage of the fourth tentacle, where it is inserted into 

 the skin and subcutaneous connective tissues. Some fibres of it certainly seemed to pass 

 on to the tentacle itself. It may be, and in fact is the more probable, that the slip only 

 fuses with other connective tissues themselves attached to the tentacle, and thus only 

 secondarily exercises what can, after all, be but a slight control over the motion of this 

 tentacle. The question of fact is not easy to determine, owing to the wealth of fibrous 

 connective tissue which is at this region confused with the tendon of the muscle. 



For the function of the copulo-glossus superficialis see the following muscle. 



17. M. copulo-glossus profundus. (Figs. 3, 9, 11, e.g. p. (Part I.), c.g.p'., c.g.p".) 



J. Muller, Innere Vorzieher cler Zunge (p. 251). 

 ,, Zioeite „ ,, (p. 323). 



Tiefe „ „ (p. 331). 



Aybrs and Jackson, Protractor of the Dental Plate (p. 203). 



This muscle arises by two heads — a large lateral head (c. g. p'.) and a smaller median 

 head (c.g.p".), and is a very long and powerful muscle. 



Lateral Head. — May arise from the posterior extremity of the ventral or keel 

 surface of the posterior segment of the basal plate, which surface is not utilised for 

 the attachment of the copulo-copularis muscle. In other specimens, and also in the 

 sections, the fibres extended laterally and posteriorly below the posterior segment, and 

 hence arose from the superficial fascia of the copulo-copularis itself. The posterior 

 segment is, however, represented behind its true termination by the tough fibrous 

 tissue of its sheath forming a median ventral strand. The most superficial fibres of 

 the lateral head meet at the mid-ventral line, and are covered externally by the rectus 

 muscle, whilst the obliquus extends over the whole. The fibres course in a weak 

 arch outwards and forwards and then downwards at the side of the median head, and 

 over the ventral surface of the basal plate, receiving in front in one specimen a small 

 bundle of fibres from the copulo-glossus superficialis. In front, the median border of 

 this head is opposed to the outer border of the rectus. 



Median Head. — Has a similar origin to the lateral head, but situated immediately 

 in front of and covered by it. The origin covers the entire surface of the posterior 

 segment at this region, but does not extend beyond it. The median head, however, 

 soon emerges from underneath the lateral one, and its fibres course outwards and 

 forwards in a still weaker curve, the two heads being closely opposed as they pass 

 forwards. At about the middle of their course the rectus muscle passes in between 

 them to reach the middle segment of the basal plate. The two median heads are 



