ON THE GENERAL MORPHOLOGY OF THE MYXINOTD FISHES. 687 



flatten out so as to become ribbon-shaped, and is opposed internally to the M. palato- 

 ettmioidalis superficialis, lying at the side of the nasal capsule. In front of the 

 capsule it courses superficially as a very broad ribbon-shaped muscle at the side of the 

 head. Anteriorly, it separates off below a small bundle which is inserted externally 

 into the sheath of the base of the third tentacle. The larger dorsal part then rapidly 

 narrows down, and is inserted externally into the basal sheath of the first tentacle. 

 It is obvious that this muscle is something more than the retractor of the first and 

 third tentacles, and in fact most of its fibres, constituting the middle portion of P. 

 Furbringer, pass straight forwards and terminate on the tough spongy tissue of the 

 snout between, and in the region of, the first and third tentacles. 



J. Muller states that in Bdellostoma this muscle arises from the palatine bar and 

 is inserted into the first, second, and third tentacles only, i.e. there is no middle portion. 

 In Myxine it is everywhere widely separated from the palatine bar, and is, further, 

 not inserted into the second tentacle. Any movement of the first tentacle, however, 

 would necessarily affect the second. P. Furbringer also queries Muller's statement 

 of the origin from the palatine bar mentioned above. The morphology of this 

 interesting muscle I leave over until its innervation is described. 



4. M. tentaculo-ethmoidalis. (Figs. 3, 10, 11, t.e.) 



J. Muller (in part), Compressor des Mundes, Mundschliesser (p. 259). 



A clearly defined muscle, coursing obliquely backwards and outwards, and com- 

 pressed from side to side into a vertical band, the dorsal border appearing behind on 

 the lateral surface above the transversus oris, and the ventral border appearing on the 

 ventral surface between the transversus oris and the copulo-ethmoidalis, but the two 

 latter muscles approximate posteriorly, and there exclude the posterior end of the 

 tentaculo-ethmoidalis from the ventral surface. It thus extends for a great part of its 

 course from the dorso-lateral surface of the snout on to the ventral surface of the same, 

 but is separated from the skin at both extremities by the elaborate blood sinuses which 

 exist at this region, and, further, it is partly covered dorsally by the upper limb of 

 the tentacularis posterior. 



The tentaculo-ethmoidalis arises mostly from the entire lateral surface of the zone 

 of soft cartilage forming the anterior end of the subnasal bar, but the origin was 

 continued also on to the same surface of the hard cartilage part. It is, however, soon 

 displaced from the latter by the copulo-ethmoidalis, when it takes up a position in the 

 extensive concavity on the external surface of the latter muscle. In the sections, and 

 especially on the right side, some fibres arise in front of the origin given above from 

 the ventro-external surface of the transverse labial cartilage. There is also in the 

 sections some confusion between the origin of the present muscle and the ethmoideo- 

 nasalis, but I could not establish with certainty any real mingling of the fibres of the 

 two muscles. 



