6 Messrs. Hancock and Embleton on the Anatomy of Eolis. 



On removing these muscles there is brought into view a very 

 thin stratum of ghstening muscular fibres, PI. I. fig. 9/, attached 

 to the opposed edges of the horny plates and converging towards 

 the oesophagus, upon which they pass, forming at once a coating 

 of longitudinal fibres for that tube, and the attachment of it to 

 the skeleton of the mouth. This delicate layer lies upon the 

 lining membrane of the mouth and oesophagus. 



On cutting through the hinge and separating the horny plates, 

 we obtain a view of the interior of the mouth, PI. I. fig. 8; here 

 we find in the median line the arched prominent ridge of the 

 tongue c, extending from before backwards, formed of seventeen 

 or eighteen transversely curved imbricated plates, PI. II. fig. 1, their 

 posterior free edges thickened, of a dark chestnut colour, and 

 presenting about forty spines slightly bent, and having their 

 points directed backwards. This ridge is supported upon the 

 curved apex of a wedge-shaped muscular mass, PL I. figs. 6/ and 

 8 dj that rises from the posterior inferior wall of the mouth, and 

 is much thicker behind than before. A lateral view of this mass 

 shows two sets of muscular fibres : one, by far the stronger and 

 larger, arising from the inner surface of the inferior posterior 

 margin of the horny plate, and radiating to all parts of the curved 

 ridge, where they are inserted into the ends of the transversely 

 arched plates which sustain the spines ; the other set, much less 

 strongly marked, and crossing obliquely over the former, arise 

 from the posterior extremity of the curved ridge of the tongue, 

 and thence pass forward to be inserted successively into the ends 

 of all the transverse plates of the ridge from back to front ; the 

 upper fibres are consequently the shortest, the lower the longest. 



The former set of fibres, when acting as a whole, will carry 

 downwards and backwards the entire ridge of the tongue. When 

 the muscles of the two sides act alternately, the tongue will 

 be moved from side to side; when the anterior and posterior 

 borders of the muscles act alternately, as it may be supposed 

 they can, the alternate advance and retreat of the spiny ridge will 

 be assisted. The degree of curvature of the tongue and the 

 situation of the curve will materially depend upon the former, as 

 well as upon the latter set of fibres. 



On removing the muscles just described from off one side of 

 the tongue, a very beautiful piece of mechanism is brought into 

 view ; we find, corresponding to the base of the tongue and the 

 under surface of the buccal mass, two strong semicircular bands 

 of muscle ; one, the inferior, PI. I. fig. 5 b, arises from the infe- 

 rior pointed extremity of the cutting-jaws e, directly above the 

 inferior transverse muscle that assists to close the jaws; and 

 thence passes in a curve backwards and upwards, and is inserted 

 into the posterior extremity of the ridge of the tongue. It is to 



