522 THE INTESTINAL CANAL, BY E. KLEIN AND E. VERSON. 



the fibres of which are all medullated, are contained in the mucous 

 membrane at the bottom of the folds. 



The transversus linguae exhibits a looser arrangement, as it extends 

 from the middle line of the upper surface to the lower, in that its 

 fasciculi describe arches, which diminish in length towards the border 

 of the tongue. 



In the tongue of ike frog the papillae filiformes are distributed over 

 the whole dorsal surface ; towards the posterior cornua they diminish 

 in number and size, and cease at some distance from their apices. 

 There is also a lateral zone of the dorsum extending along the whole 

 length of the tongue, and from two to three millimeters in breadth, 

 which is destitute of papillae. The fungiform papillae are similarly 

 arranged. The two forms are most numerous and largest at the 

 anterior part of the dorsal surface. The papillae filiformes are thin and 

 long, but towards the cornua of the tongue they are somewhat broader. 

 The epithelium, throughout the entire cavity of the mouth, consists of 

 a laminated and ciliated columnar epithelium, with the exception 

 of the apices of the papillae, where the most superficial cells are short 

 cylinders, destitute of cilia.* Neither Hartmann nor Hoyerf were 

 able to recognise the continuity of the processes of the columnar 

 epithelium covering the papillae with the connective tissue corpuscles, 

 as described by BillrothJ and Axel Key. 



On the lower surface of the tongue the epithelium is formed by two 

 or three layers of pavement cells, the most superficial in some parts 

 bearing cilia. 



A nerve trunk, composed of dark-edged fibres, occupies the centre 

 of the fungiform papillae, whilst at their periphery is a capillary 

 plexus opening into a central vessel ; situated peripherally also are 

 muscular fibres which frequently undergo division in their passage 

 upwards. Moreover, transversely situated muscular fibres extend 

 into the fungiform, and into some of the filiform papillae, though they 

 can seldom be followed to the apex. 



The glands of the tongue of the frog are pretty equably distributed 

 over the whole of the dorsal surface ; anteriorly they are more closely 

 assimilated to the type of the acinous glands than posteriorly. The 



* Ley dig, Histologie, 1857, p. 307. Axel Key, Reichert and Du Bois' 

 Archiv, 1861, p. 228. Hartmann, idem, 1863, p. 634. 



t Hoyer, Mikroskopische Untersuchungen uber die Zunge des Frosches, 

 Reichert and Du Bois' Archiv, 1859, p. 501. 



| Ueber das Epithel der Froschzunge, Miiller's Archiv, 1859, p. 159. 



Waller, Philosophical Transactions, 1847. 



