MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 157 



into the base of the depression running- back from the radolar opening. Outside of this is 

 another flat muscle, the radular (R), having its origin just in front of the internal lingual. It 

 runs forward and inward, and, uniting with its fellow on the opposite side, is attached to the 

 anterior side of the ascending portion of the radular sac. Above the two muscles just described 

 is a very much larger muscle which forms the bulk of the tongue. To this I have given 

 the name external lingual (EL). Its origin lies above the origins of the other two muscles. 

 From this it runs forward and upward and inward, partly to join its fellow of the opposite side 

 in forming a sling which covers the whole of the ascending portion of the radular sac anteriorly, 

 and partly to be inserted dorsally along the ridge of the tongue. The sling formed by the exter- 

 nal Unguals in front of the radular sac is not attached to the latter in any way. These three 

 muscles do not have their origins upon any hard part, such as the jaws, but in a sort of tendinous 

 mass (T), which is firmly attached to the floor of the mouth and the muscular membrane described 

 a short time ago. From this tendon a short, strong muscle, the lingual protractor (LP), runs 

 forward and outward under the edge of the opening muscle of the jaws (Fig. 33, 8) to the pro- 

 jecting point of the inner flange of the upper jaw. It would seem as if the only effect of the 

 contraction of this muscle must be to pull the origin of the lingual muscles forward, possibly 

 permitting a greater extension of the tongue; the combined effect of the contraction of the inter- 

 nal and external lingual and the radular muscles would be to pull the tongue and the radula up 

 and back; a simultaneous contraction of the lingual protractor would possibly keep the radula 

 tightly pressed against the object it was rasping. The sling formed by the external lingual is 

 not attached to the radular sac in any place. The integument which supports the free portion 

 of the radula is strongly supplied with muscle fibres running outward and downward to the sides 

 of the jaw; the distinct muscles going to these parts have been mentioned. While these muscles 

 are comparatively weak, they probably are protractors of the tongue. For the structure of 

 the radula indicates that its rasping or pulling effect is produced only when the tongue is thrust 

 upward and backward, and only in this motion would great resistance be encountered. Conse- 

 quently the muscles which pull the tongue back are large and strong. As no great resistance 

 would be encountered in pulling the tongue forward, the small muscles attached to the integu- 

 ment seem to be sufficient. The integument of the tongue is supplied with a weak longitudinal 

 musculature. 



Small muscles extend into the salivary lobes from near the origins of the lingual muscles. 



The walls of the mouth cavity are formed by the inner flange of the upper jaw, except 

 vent-rally. From the floor of the mouth the tongue, bearing the radula, and four fleshy processes, 

 project into the cavity. In front of the tongue are two processes (Fig. 32, PP and AP), one 

 behind the other, which are really upfoldings of the floor of the mouth. The anterior process 

 is 8 millimeters in height and 12 millimeters in width, covered with papilla? upon both sides, the 

 papilla 1 upon the anterior side being much smaller than those upon the posterior side. The 

 posterior of the two processes is slightly higher and considerably wider than the anterior. Its 

 base is carried up a short distance on each side of the tongue. This process bears papilla? only 

 upon the edge and the posterior side; the anterior surface is covered with fine transverse ridges. 



The tongue is a large organ which occupies most of the space within the mouth. (Fig. 32. Tn.) 

 It is about 22 millimeters in length, 10 millimeters in width, and 15 millimeters in height. 

 Anteriorly the tongue rises abruptly and with somewhat of an overhang to its full height. For 

 nearly half its length it maintains this height, then slopes gradually to the floor of the mouth, 

 immediately in front of the esophageal opening. The shape of the tongue may vary, e. g., it 

 may slope downward and forward to the opening of radular sac, and then sloping down and back. 

 The sides of the tongue are nearly vertical and are entirely free from papillae. The dorsal surface 

 of the tongue, on the other hand, is thickly covered with large papilla-. Just in front of the 

 (esophageal opening are a number of peculiarly long and slender papillae. 



The anterior surface of the tongue, is covered by the radula. (Fig. 32, R.) The radula passes 

 up over the tip of the tongue and then almost immediately bends downward again and is lost to 

 view in the radular sac. The radular sac passes downward and a little backward under the 

 integument of the point of the tongue till it reaches the under side of the tongue, where it abruptly 



