ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 701 



by approximating the basal plate and subnasal bar. This will facilitate the rasping 

 action of the ventral teeth. 



15. M. hyo-copulo-glossus. (Fig. 11, h. e.g.) 



J. Muller, Beuger des Zungenbeins (p. 249). Beuger des ersten und ztoeiten Gliedes des 

 Zungenbeins (p. 332). 



A powerful flat longitudinal muscle which arose in a 34|- cm. Hag from the anterior 

 surface of the most ventral 2| mm. of the first branchial arch internal to the insertion 

 here of the hyo-copulo-palatinus, but in another specimen of the same size from the most 

 ventral 3|- mm. This origin from the first branchial arch is wanting in Bdellostoma 

 according to J. Muller. In the sections the most dorsal fibres were so intimately 

 associated with the insertion here of the hyo-copulo-palatinus that I am doubtful 

 whether they can be separated. Some fibres also may arise from the middle segment 

 of the basal plate anterior to where the first branchial arch fuses with it. The fibres of 

 the muscle at first pass forwards and slightly upwards, almost parallel, but slightly 

 converging, and alongside and external to the middle segment of the basal plate. 

 Opposite the anterior border of the broad forward ventral process from the hyoid arch 

 described on p. 764 of my first Part, and shown in fig. 2, and which I now believe to be 

 of general occurrence (cp. fig. 11 of present Part), the muscle on the right side in the 

 sections received a small reinforcing head from, the inner surface of the membrane 

 connecting the pharyngeal basket with the basal plate. This was also suggested on the 

 left side. The fibres now fan out and take a more dorsal course, and are inserted partly 

 into the fascia investing the mucous membrane of the lateral diverticulum of the mouth 

 at the base of the dental apparatus (opposite about the dorso-middle region of the 

 latter), but also largely into the loose ventral fascia between the dental skeleton and the 

 basal plate and which is attached in front to the mucosa of the ventral region of the 

 mouth. The pull on the ventro-lateral mucosa naturally retracts the fourth tentacle 

 also, and this is doubtless the basis for the statement by J. Muller and P. Furbrinoer 

 that the " tendon " of this muscle is inserted into the fourth tentacle. In another 

 specimen a few of the most posterior fibres extended on to the mucosa of the roof of 

 the mouth, and this was observed in sections also. 



Opposite the antero-ventral angle of the belly of the hyo-copulo-glossus, which here 

 sends downwards a small projection, there is a wide strand of fatty connective tissue, 

 which passes upwards and inwards to fuse with the stout membrane connecting the 

 anterior and posterior arches of the dental plate about midway between these two 

 cartilages. It is itself not ligamentous, but in the sections it assisted in transmitting 

 an inconsiderable bundle of elastic fibres which arose from the tissues around the 

 posterior arch of the dental plate and passed forwards (fused in front of the "tether" 

 with the ventral free margin of the " tendon " of the hyo-copulo-glossus) to be inserted 

 into the dorsal margin of the guiding rail on the anterior segment of the basal plate 



