142 



BIOLOGICAL LECTURES. 



description of it here. It will suffice if I confine my remarks 

 to the large club-shaped muscle which lies between the 

 anterior pairs of gills. In cross section the muscle is seen to 

 be composed of an outer thin ring — the section of the thin 

 cylindrical muscle, and an inner solid muscular disc — the sec- 

 tion of the solid, club-shaped muscle, which is made up of two 

 equal lateral halves. Johannes Miiller has called the outer one 

 of these the hollow tongue muscle, and it certainly does at 

 first sight seem to deserve the name. 



The long tendon into which the tongue muscles taper, runs 

 forward in a groove in the top of the cartilaginous floor of the 

 mouth until it reaches the posterior border of the tongue, when 

 it splits up into two unequal bundles of tendinous fibrillae, 

 which run forward and insert into the upper surface of the 

 tono-ue bodv. These slender tendinous slips are so arranged 

 that, when the tongue is drawn out of the mouth, the carti- 

 laginous bars carrying the teeth are turned, so as to throw 

 the teeth outwards and forwards in such a manner that their 

 points are erected, and catch readily the instant the club- 

 shaped muscle begins to draw it back into the mouth. The 

 teeth are corneous structures,^ borne upon the soft teeth 

 'papilhe, and the teeth of any one row are more or less fused 

 tojrether at their bases, so that w^hen separated from their 

 papillae, they hang together in a row or plate. (Figs. 4 and 5.) 

 Oftentimes, the inner tooth, which is also the larger, separates 

 from the others, and the outermost tooth of the row is not 

 always united with its fellow. Each tooth is an exceedingly 

 sharp-pointed, conical body, flattened from above downwards, 

 and curved from without inwards. 



1 I have made a special examination of the teeth of Bdellostoma dombeyi and 

 Myxine glutinosa, and although I was desirous of finding the enamel cap described 

 by Beard I was unable to do so. There is not the slightest trace oiboitc in any of 

 the teeth of these two forms, and what I'-eard has taken to be such is doubtless 

 much hardened horn, produced by the methods used by this author in preparing 

 sections of teeth for microscopic examination. I have cut a large number of the 

 teeth of Bdellostoma and of Myxine and have found no difficulty in sectioning 

 them in situ when imbedded in celloidin. The Myxinoid teeth are cornefied 

 sheaths of the epidermal elevations on the tongue plate, and in adult life show no 

 trace of dentine or enamel. 



