ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 



741 



Size of Hag in cm.'s. 



20J 



221 



24i 



26£ 



28 



37 



Left and Right Sides. 



L. 



R. 



L. 



R. 



L. 



R. 



L. 



R. 



L. 



R. 



L. 



R. 



Anterior to Branchial Pore 

 Opposite Branchial Pore . 

 ) Between Branchial Pore and Cloacal 

 Aperture ..... 

 Opposite Cloacal Aperture 



28 

 1 



56 



2 



20 



28 

 1 



57 



2 



21 



28 

 2 



53 



2 



22 



27 

 1 



53 



2 



22 



27 



2 



54 

 2 



20 



27 

 1 



54 



2 



21 



29 



2 



59 



2 



19 



29 

 1 



60 



2 



20 



30 



2 



57 

 2 



24 



30 



1 



58 



2 



25 



30 



2 



56 



3 



20 



28* 

 1 



58 



2 



22 



Total 



107 



109 



107 



105 



105 



105 



111 



112 



115 



116 



111 



111 



* Of these the first was partially subdivided into two, and obviously corresponded to the first and second of the left side. 

 Hence there is really one more on the right side than on the left. 



first myotome is doubtless the one with the posterior extension, the small quadrangular 

 one being additional. I have, however, never seen any appreciable dorsal section to 

 the first myotome except in one case (see fig. 9), where a few scattered fibres in front 

 of the second myotome might have represented the dorsal portion of the first. When 

 the first myotome is quadrangular it is entirely covered by the dorsal extension of the 

 obliquus, but when the posterior extension is present, this is visible as far as it is 

 developed after removal of the skin. In all cases the first myotome is considerably 

 smaller than the succeeding ones, and never extends so far ventrally. According to 

 J. MtiLLER, the first myotome is attached to the " cartilage process at the anterior end 

 of the tongue bone and to the cartilage of the ventral [fourth] tentacle." This is very 

 different from Myxine. 



The normal second myotome is in some exceptional cases, as stated above, preceded 

 by two distinct myotomes, in which case, of course, it becomes the numerical third. 

 The first is then very small, whilst the second represents the normal first myotome. 

 The normal second myotome consists of two limbs, placed at about a right angle, with 

 the apex directed posteriorly. The dorsal limb passes upwards and forwards behind 

 the posterior extremity of the tentacularis posterior, but does not reach the mid-dorsal 

 line (figs. 8 and 9). The ventral limb courses downwards and forwards, at first under 

 the ventral border of the tentacularis posterior, but afterwards behind and below the 

 first myotome. There is a distinct furrow between the second myotome and the 

 tentacularis posterior. Myotomes three to about eight or ten vary in external 

 appearance, and have the form indicated in figs. 8 and 9. From myotome ten up to, 

 generally, about twelve from the tip of the tail, all the myotomes exhibit the following 

 external conformation (fig. 5). At the side of the mid-dorsal partition there appears to 

 be a continuous narrow muscular band, unbroken by any septa intermuscularia. If this, 

 however, is examined carefully in Perenyi-fixed material, it will be seen that it is 

 traversed by very faint septa, which pass very sharply backwards. The septa then 

 become obvious, and turn sharply forwards at an acute angle, then backwards again at 

 a somewhat less acute angle, and finally by an obtuse angle pass downwards and 

 slightly forwards. This agrees substantially with J. Muller's description and figure of 

 the tail region of Bdellostoma. On the body the arrangement is simpler, according to 



