1 86 ON THE MORPHOLOGY OF THE CEPHALOUS MOLLUSCA 



He gives the name of tongue exclusively to a " bifid papillose 

 organ, surrounded by circular folds, which consists mostly of vascular 

 branches, between which masses of muscle are interwoven '' : this is 

 placed in the floor of the buccal cavity in front of and below the buccal 

 mass. 



To what is commonly known as the tongue, he gives the name of 

 " radula," " reibplatte." The dentigerous plate is the " lamina radulae," 

 its expanded portion the " orbis radulje." What I have called the 

 buccal cartilages are his " folliculi motores.'' 



It is difficult to come at any clear understanding of Middendorfs 

 views, but so far as I can comprehend them, he appears to consider 

 that the " lamina radula; " acts as a sort of elastic file pushed from 

 behind by a special muscle, the " curvator radulas," and supported and 

 steadied by the " folliculi motores." 



Von Siebold says,i " this organ (the tongue), by its protrusion and 

 retraction, is made use of by the Cephalophora as an ingestive appa- 

 ratus." He says nothing about the buccal cartilages or the minute 

 structure of the organ. 



When I first examined this apparatus carefully six or seven years 

 ago in Buccimivi, I was convinced that Cuvier had mistaken its mode 

 of operation, and further observation has only strengthened that con- 

 viction. 



I have already described the manner in which the apparatus may be 

 seen working in Firoloides and Atlanta, and I propose now to demon- 

 strate that from the anatomical arrangements the " tongue " has the 

 same chain saw-like mode of operation throughout the Cephalopoda 

 and Gasteropoda. Perhaps Patella may be taken as the most con- 

 venient illustration, since the organ is here very large, and its parts are 

 distinct and well -developed. 



In Patella (Plate V. [Plate 20] figs. 12, 13) it is an oblong mass, 

 reddish, except where the tongue-plate shines with a somewhat 

 greenish hue. It is bifid posteriorly, and has a sulcus along two-thirds 

 of its upper surface. In this the tongue lies before it enters the 

 cavity of the mouth. The opening of the oesophagus corresponds 

 with about the anterior fourth of the upper surface of the buccal mass. 



To the postero-lateral angles of the mass its extrinsic protractor 

 muscles are attached, two on each side. They go to be inserted into 

 the cephalic parietes, two in front of and above, and two behind the 

 supracesophageal ganglia. The lower ones are united so as to form a 

 broad muscular plate. Two small muscular bands are also sent from 

 the anterior angles of the buccal mass to the skin of the head. 



^ Vergleichende Anatomie, p. 320. 



