308 PROFESSOR FRANK J. COLE 



when the latter is withdrawn. It is mentioned by J. MtJLLER. I do not find any 

 special histological feature associated with it. 



The lining of the naso-pharyngeal canal behind the nose is quite smooth and 

 without valves. When the canal is split up and the nose examined from below, it is 

 found that the median olfactory lamina is deeper and thicker, and has a more 

 pronounced free margin than the others, and thus, in a sense, separates the apparently 

 single nasal organ into two. The posterior portion of the third lamina from the middle 

 on each side appears to have a somewhat valvular character, and would tend to direct 

 water upwards among the laminae in general. The lining of the nasal tube in front 

 of the nose is almost smooth, and has no definite folds ; but there is a well-defined 

 transverse fold and a slight median dorsal longitudinal fold just in front of the nose 

 itself, whilst dorsally and medially, just inside the external nasal opening, there is a 

 blunt projection supported by a small independent cartilage (fig. 1, present part; and 

 figs. 1, Parts I. and III.). 



From the Jloor of the mouth there projects into its cavity the dental apparatus, 

 consisting of two halves separated by a furrow or gutter. The mucosa is reflected over 

 the bases of both rows of teeth, but more particularly over that of the outer row, whilst 

 the two rows of each side are separated by another and very distinct fold of mucosa, 

 the tips of the outer teeth being almost on a level with, or projecting slightly beyond, 

 it. The dental apparatus is obviously a derivative of the mucosa of the floor of the 

 mouth, and cannot move independently of it. Therefore, to admit of any movement 

 at all, the mucosa in front of and behind it must be loose and ample. When the 

 apparatus is withdrawn there is an obvious transverse folding or puckering of the 

 posterior mucosa (which was previously on the stretch), whilst the mucosa in front is 

 quite taut. Behind this give-and-take region the mucosa of the floor of the mouth is 

 thin and almost smooth. Again, the margin of the mouth is always puckered when 

 the dental apparatus has been withdrawn, but when it is everted there is a pleated area 

 ventrally outside the mouth, which is not fully shown in any figure I have seen. In 

 the retracted condition there is a raised zone of mucosa extending straight forwards over 

 and in front of the protractor tendon, and which in places is very sharply folded — in 

 fact, so much so that one often has to separate the lips of the depressions with a needle 

 before they are noticed. These occur nowhere else in the mouth. They seem to me 

 to be due to the fact that when the pre-dental mucosa is drawn into the mouth it is 

 compelled to occupy a much narrower space laterally than it does when outside 

 the mouth. 



The mucosa of the floor of the mouth is practically smooth. 



F. Histology of tru Gut. 



The histology of the alimentary tract of Myxine has already been described and 

 figured by K. E. Schreiner, and especially by Maas. The latter has investigated the 



