ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 719 



reduced or even absent, but I have never encountered this variation either in my 

 dissections or sections. 



A fairly powerful and apparently club-shaped muscle, with the handle directed 

 backwards, and the whole covered externally by the parietalis. The shape is due to 

 the fact that whilst the dorsal half of the fibres passes straight back to its insertion, 

 the ventral half bends inwards and slightly upwards at a right angle between the 

 copulo-glossus superficialis ventrally and the constrictor pharyngis I. dorsally to reach 

 its insertion, which is thus internal to the dorsal half. 



The anterior extremity of the muscle arises — (a) from the fascia of the dorso- 

 posterior border of the hyo-copulo-palatinus ; (b) from the fascia of the dorso-posterior 

 portion of the copulo-quadratus profundus ; (c) from the fascia connecting the superior 

 and inferior processes of the pterygo-quadrate (in the sections) ; and (d) largely from 

 the inferior process of the pterygo-quadrate itself. From its origin, the muscle passes 

 backwards and somewhat downwards, crosses transversely the cranio-hyoideus and 

 constrictor pharyngis I., and finally bends inwards over the copulo-glossus superficialis 

 in front, and over the lateral head of the copulo-glossus profundus for a short distance 

 behind, to be inserted as follows : the dorsal half of the fibres is inserted partly into the 

 ventro-lateral fascia of the anterior extremity of the copulo-copularis, but also largely 

 into the dorsal margin of the posterior segment of the basal plate from the beginning 

 of the taper backwards, and dorsal to the origin of the copulo-glossus superficialis, 

 which for a time may even exclude it from the basal plate. For a short distance 

 posteriorly (in the sections) it was wedged in between the lateral head of the copulo- 

 glossus profundus and the copulo-copularis ; the ventral half of the fibres is inserted 

 into the dorsal margin of the posterior segment of the basal plate in front of the above, 

 i.e. from the beginning of the taper forwards. The whole origin in a 35 cm. Hag 

 extended over 7 mm. of the posterior segment. It must be remembered that the 

 latter is here U-shaped, and that, therefore, the dorsal margin on each side is a free and 

 somewhat thin border. 



According to J. Muller in Bdellostoma, the copulo-quadratus superficialis is 

 " inserted " into the margin of the palatine bar where this passes over into the 

 pharyngeal basket. As P. Furbringer points out, this " insertion " is carried much 

 further forwards than in Myxine ; and as the basal plate is the movable point, it is as 

 well to call that extremity of the muscle the insertion. 



The function of this muscle seems to be the same as that of the hyo-copulo- 

 palatinus. 



24. M. copulo-quadratus profundus. (Fig. 3, c.q.p.) 

 J. Muller, Zuriickzieher des Zungenbeins (p. 249). 



A very wide, powerful muscle, situated mostly under the hyo-copulo-palatinus, and 

 in part just external to the mucosa of the mouth. It has an irregular or ragged dorsal 



