ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 715 



protractor acting on the mucosa and teeth, and the deep protractor acting on the 

 dental skeleton itself. Although the withdrawal of the apparatus is obviously a simple 

 process, and is in point of fact effected by one muscle, the longitudinalis linguae, 

 nevertheless the division of the tendon of this muscle is of such a nature as to roughly 

 antagonise the pull of the two protractors. The median ventral tendon corresponds to 

 the deep protractor, and acts directly on the dental skeleton. The paired dorsal tendons 

 correspond to the superficial protractors, and act rather on the mucosa posterior to the 

 teeth. The protractors and retractor may, of course, represent one muscle, with the 

 dental skeleton as a sesamoidal deposit. Cp. the function of the protractor muscles. 



20. M. perpendicularis. (Figs. 2, 3, pp.) 



J. Muller, Innere senkrechte Muskel der Zunge (p. 257). Senkrechter Muskel des Zungen- 

 muskelapparates (p. 331). 



This is an unpaired median vertical muscle, and courses between and separates the 

 posterior ends of the two longitudinalis linguae muscles like a rod pushed through a 

 loop. It is a short but powerful muscle, wide antero-posteriorly, and slightly com- 

 pressed from side to side. In transverse section it is somewhat pear-shaped, with the 

 narrow end anterior. In a 34 cm. Hag it had a maximum width of 5 mm. and height 

 of 7 mm. It arises from the dorsal and lateral surfaces of the posterior two-thirds of 

 the inferior chondroidal bar, and its parallel fibres pass upwards and somewhat forwards 

 to be inserted into the middle ventral surface of the superior chondroidal bar, i.e. 

 except for a short region anteriorly, and the lateral zones occupied by the dorsal fibres 

 of the longitudinalis linguae. 



The function of the three muscles constituting the retractor apparatus of the 

 "tongue" is a subject of as considerable interest as the apparatus itself is unique. 

 The longitudinalis linguae has been dealt with already, so that it is here only a question 

 of the other two. According to J. Muller, the perpendicularis, by compressing 

 flat the posterior end of the muscle mass, fixes this end of the longitudinal muscle, 

 whilst the latter, by drawing the dental apparatus sharply back, enables the ventral 

 teeth to scratch and file away the prey already fixed by the palatal tooth. The 

 copulo-copularis is stated to fix the longitudinal muscle in the retracted condition ; 

 but Muller is undecided whether the contraction of the constrictor muscle might 

 not also squeeze the longitudinal muscle out, and thus assist in everting the dental 

 apparatus. On the other hand, P. Furbringer regards the constrictor muscle as 

 a powerful supporter of the protractors of the " tongue," but agrees that the vertical 

 muscle fixes the longitudinal muscle at its posterior end. To quote his own words, he 

 says (p. 24) — " Durch die Contraction des Hohlmuskels wird zunachst der Hohlraum 

 derselben erheblich verengt ; dieser Volumenreduction muss nattirlich auch der Langs- 



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