ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 721 



25. M. vdo-quadratus. (Figs. 3, 7d, 11, 12, v. q., v. q'., v. q".) 

 J. Muller. AnzieJier des Schlundsegeh (p. 260). 



I describe this muscle as dissected from the ventral surface. It is an extensive 

 and irregular muscle, with its fibres arranged into coarse fasciculi, and the fasciculi 

 grouped into three perfectly distinct divisions (both in dissections and in the sections), 

 which might almost be described as three separate muscles. 



Ventral Division (v. q.). — Arose in one dissection — (a) from the lateral margin of 

 the central expanded portion of the hypophysial plate ; (b) from the tough tissue 

 between the latter plate and the ptery go-quadrate ; (c) from the internal surface of the 

 pterygo-quadrate at, and in the immediate neighbourhood of, the zone of soft cartilage 

 between the palatine bar and the pterygo-quadrate. In the sections a small portion 

 of the fibres arose from the stout membrane connecting the hypophysial plate with 

 the anterior extremity of the soft cartilage portion of the trabecula. The origin then 

 passed on to the lateral margin of the above plate immediately before this fused with 

 the rod from the nasal capsule. The receipt of the latter adds to the width of the 

 plate, so that the ventral division, since it continues its origin straight backwards, no 

 longer arises from the lateral edge of the plate, but from the ventral or external 

 surface of it, not quite half way down. When, however, the trabecular connection is 

 given off from the plate, # the muscle again arises from its lateral margin, until it is 

 displaced from it by the anterior extremity of the origin of the dorsal division. There 

 were no signs of any origin from the pterygo-quadrate. 



The fibres of the ventral division pass backwards and outwards, and finally 

 converge to be inserted into the ventro-external portion of the anterior or free surface 

 of the expanded head of the external lateral velar bar. The ventral division almost 

 entirely covers the middle division ventrally, but the dorsal division appears behind 

 at its median margin. 



Middle Division {v. q'.). — Arose in the same dissection — (a) apparently from the 

 cranium slightly behind the level of the origin of the ventral division ; (b) from the 

 ventro-internal surface of the anterior end of the trabecula. In the sections it arose 



(a) from the ventral surface of the anterior soft cartilage portion of the trabecula ; 



(b) from the same surface of the naso-trabecular cartilaginous commissure at and in 

 the neighbourhood of its fusion with the hypophysial plate ; (c) from the tough 

 membrane between the latter plate and the trabecula ; (d) from the ventro-internal 

 surface of the zone of soft cartilage between the pterygo-quadrate and the palatine bar. 



The fibres of the middle division pass backwards and outwards, and converge 

 slightly to be inserted into a knob of soft cartilage at the dorso-external margin of 



* The correct view to take of these cartilaginous fusions is that they represent a connection between the olfactory 

 capsule and the trabecula which fuses with the hypophysial plate on the way. This is also suggested by Neumayer's 

 figure and by my own sections. 



