8 MIXOT ON THE TONGUE 



on the dorsal surface ; it is especially thickened in the median dorsal line, again just over 

 the upper and outer corners of the muscular core, and in the furrow. Still further 

 forward there are also two thickenings, fig. 7, on either side below the furrow. As these 

 thickenings all appear upon many successive sections, they must each correspond to a 

 longitudinal ridge. Along the ridges and the two furrows, the corneous layer is 

 represented by a stratum of somewhat flattened cells. The main thickness of each ridge 

 is occupied by lai'ge polygonal cells, which in the basal part, become cylinder-cells, and 

 are there mingled with smaller cells with smaller nuclei. Thus, on the inner surface of 

 the epithelium, there are seven longitudinal ridges, distinguished by their histological 

 character. As the thickenings in the furrows resemble the ridges, except in their position, 

 it seems to me correct to call them ridges also, — making nine in all, as follows : — three 

 dorsal, hvo in the furrows, four lateral below the furrows. None of these ridges extend 

 upon the forks of the tongue. 



A short distance behind the fork, the epithelium on the under side assumes a follicular 

 character, the corneous layer becomes very thin, while the mucuous increases in thickness, 

 fig. 14. The cells of the middle portion are quite distinct, and have polj-gonal outlines ; 

 they are of two kinds, one smaller, with nuclei of the usual character, the other larger 

 with clear vesicular nuclei. The basal or follicular portion consists of much smaller 

 cylinder cells, some with pale oval, others with long darkly stained nuclei. 



Upon the base of the forks the epithelium, fig. 15, has the general character shown in fig. 

 14, except that the middle layer of polygonal cells is more distinctly separated into an 

 outer and inner structure, the cells of the former being flattened. The follicles partially 

 disappear a short distance from the base of the fork. 



The muscles of the tongue are all intrinsic, excepting the ceratoglossi, and are five in 

 number, counting the paired muscles once only. They all lie in close proximity to one 

 another, forming a continuous fleshy mass, the muscular core, occupying the centre of the 

 tongue, and invested by a common fascia or sheath, into which the muscular fibres are 

 inserted. The general appearance in transverse sections has been described above. 



The courses and proportions of the various muscles can be most readily followed upon 

 a series of transverse sections, figs. 5-11. Fig. 5 is the most anterior, fig. 11, the most 

 posterior section figured. Figs. 5-9 are through the free part of an extended, 

 figs. 10-11 through the attached part of a retracted tongue. The transverse lines 

 through fig. 1, show approximately the level at which the sections were taken, the lines 

 being numbered to correspond with the figures. Fig. 1 represents the tongue of Crotalus 

 diirissus, while all the sections are from Ancistroclon. 



The 31. ceratoglossi arise from the posterior ends of the hyoid cornu, between which 

 they run, each entirely isolated from its fellow, forward to the point, fig. 1, c, where the 

 hypoglossal nerve enters the muscle ; at which spot they become encased by the superior 

 and inferior transverse muscles, and separated from one another by the 3f. verticalis, 

 fig. 10. It may properly be said that at this point they enter the tongue, through the 

 length of which they extend, nowhere mingling with or penetrated by other muscles, or 

 by each other.^ At first the muscle occupies the largest part of the tongue ; it lies on 



1 In the Crocodilia the two genio-glossi cross one another fig. 3), has described and illustrated. The same pecuhar 

 in a peculiar manner, which Duvernoy (VI, p. 17, pi. V, arrangement maybe readily observed in the alligator. 



