ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 779 
very curious device the rasping action is, of course, made immensely effective, and a few 
Hags will completely clear out a full-sized cod in an hour and a half. I shall give a 
full description of the process in my second part on the muscles, but in the meantime 
one may point the moral that to make physiological deductions from anatomical data is 
attended with some risk. 
The dental skeleton is composed entirely of soft cartilage, except the greater portion 
of the posterior arch, which consists of hard cartilage. It commences in front as an 
irregular deposit of soft cartilage in the tendon of the M. copulo-glossus profundus,* and 
is at first almost flat, but slightly arched (with the concavity dorsal), taking no part in 
supporting the first tooth of the outer row, which is raised up almost at right angles to 
it. The cartilage soon widens out, and despatches a process forwards on each side to 
support the anterior teeth of the outer row (0. 7, t.). This is the anterior arch of the 
dental plate (a. d. p.), and it at once assumes the characteristic shape of an obtuse V, 
the teeth resting on the inner surfaces of the two arms. The tendon of the M. copulo- 
glossus profundus (c. g. p.) widens out very considerably behind, to be inserted into 
practically the whole of the anterior border of the anterior arch of the dental plate 
(fig. 7), the posterior wide portion of the tendon consisting of a tissue very similar to 
soft pseudo-cartilage. The anterior “ fine comb of horny spikes” described and figured 
by Parker in Mysxine, but not in bdellostoma, is nothing more than this tendon cut 
across (cp. figs. 7 and 10). The arch never extends laterally beyond the bases of the outer 
row of teeth, and hence its lateral surface has a curve similar to that of the fused bases 
of this row of teeth. Both rows of teeth with their papillae may be said to rather rest 
on the arch, since they are only loosely attached to it. The dental skeleton is, in fact, 
always more or less completely separated from the teeth, as emphasised by J. MU.uER, 
by a series of spaces sometimes containing blood. I have not yet investigated the 
vascular system of the head, and therefore cannot say whether these spaces are blood 
sinuses or not. The anterior arch bears two fenestre, and as I find these both in 
dissection and in serial sections, they must be of constant occurrence. The larger one 
is elongated from before backwards so as to almost divide the anterior arch into two, 
and is covered over by fibrous tissue, while the smaller one transmits the nervus 
dentalis of J. Mttuer. The postero-external angle of the arch gives off two rods— 
the posterior external (a. d. p.’) and the posterior imternal (a. d. p.") processes of the 
anterior arch. The former is plate-like and much the larger of the two, crossing over 
the latter dorsally to it, and courses inwards and upwards in the fold of mucous 
membrane situated over and almost obscuring the posterior teeth of the mner row 
(z. r. t.), to terminate blindly in this fold immediately dorsal to the last tooth of the 
inner row. ‘The internal process is a small rod which passes almost straight backwards 
below the external border of the inner row of teeth, and finally turns inwards to fuse 
with the posterior arch of the dental plate. The product of this fusion then continues 
backwards as a stout rod (turning slightly upwards) along the ventro-lateral border of 
* This is the ‘median dorsal bar’ of AyERs and Jackson. It is, of course, ventral. 
