ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 713 



not fuse. The entire mass is oval in transverse section. Dorsally, the division between 

 the two muscles can be traced almost to the tendon, but ventrally the anterior third 

 shows at the middle line a ligamentous cord, which is apparently continuous with the 

 tendon of the muscle in front. The fibres converge gradually both laterally and 

 vertically as they pass forwards, so that the whole muscle resembles a tapering pointer. 

 Its depth behind in a 34 cm. Hag was 7 mm. and its width 9 mm., whilst the entire 

 length of the muscle belly was 35 mm. The anterior half of the muscle, consisting of 

 larger and less concentrated fibres, is spindle-shaped, and its pointed posterior end is 

 buried in the anterior end of the posterior half (cp. the detailed description of the tendon 

 below). The fibres of the latter half, therefore, are inserted into the outer tendinous 

 surface of the buried end of the anterior half. Hence there is a fresh origin of 

 (histologically different) fibres to form the anterior half of the muscle. 



The belly of the longitudinalis linguae passes into a strong laterally-compressed 

 tendon, with a maximum depth in the above specimen of nearly 2 mm. This tendon 

 courses straight forwards to the dental apparatus, slightly increasing in bulk as it 

 proceeds, and having a length of 15 mm., to be inserted (in one dissection) as follows : — 

 (a) examined dorsally, the tendon split so as to give off a pair of largish lateral bundles. 

 These rapidly diverged, and were inserted mostly into the lateral portion of the posterior 

 arch of the dental plate (Part I., fig. 9). Some of the superficial fibres, however, 

 crossed over the posterior arch, traversed the space between the two arches, and were 

 inserted into the anterior arch of the dental plate. These have been dissected away 

 in the above figure. P. Furbringer states that all the fibres are inserted into the 

 anterior arch (cp. the description of the tendon from sections below) ; (b) examined 

 ventrally, the greater portion of the tendon formed a powerful median bundle, which 

 passed forwards and expanded somewhat to be inserted into the median portion of 

 the posterior arch of the dental plate (Part L, fig. 7). Here again the most super- 

 ficial fibres crossed the posterior arch and the space in front, and were also inserted 

 into the anterior arch, 'becoming there continuous with the superficial fibres of the 

 copulo-glossus profundus, as described under that muscle (not shown in fig. 7 above). 



I now describe the formation and insertion of the tendon as seen in my large series 

 of sections, which disclose a very interesting state of affairs (cp. particularly the series 

 of transverse sections given in fig. 6). 



The tendon of the longitudinalis linguae really commences far back in the interior 

 of each division of the muscle at about section 1885 (the muscle itself extends back 

 to 2287) as a vertical slip, with an inclination towards the middle line (1750, a). As 

 we pass forwards these slips increase in length, and bend more towards the middle 

 line, whilst a second more ventral pair are added (1570, 6). The next stage is the 

 fusion of both pairs of slips, the first pair to form a large half loop the ventral 

 extremities of which now appear on the surface of the muscle, and the second pair to 

 form a median vertical partition, with at first a ventral fork to indicate its paired origin 

 (1498). The hoop encloses the larger and more spongy muscle fibres forming the 



