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



of considerable size, which are either occupied by thin-walled large 

 vessels, or, being lined with epithelium, probably belong to the lym- 

 phatic system. Amongst these fasciculi extending towards the surface 

 are found a variable number of fusiform elements, with rod-like or 

 elongated nuclei. These are directly continuous with the fusiform 

 cells of the innermost fasciculi of the external muscular layer, and are 

 consequently to be regarded as smooth muscular fibre cells. 



There is consequently here no independent muscularis mucosae. In 

 the small and delicate meshes of the mucous layer, large, irregular, or 

 spheroidal masses of protoplasm lie isolated from one another. 



The external muscular layer consists exclusively of smooth muscular 

 fibres, the contour of which is either rectilinear or sinuous, and which 

 contain an elongated and often pointed nucleus. It is not everywhere 

 of equal thickness, and does not throughout its whole circumference 

 consist of two distinct layers ; on the contrary, the external fasciculi 

 interlace to a considerable extent with the internal, so that in trans- 

 verse sections a close network of muscular fibres is found, interrupted 

 only by a small quantity of connective tissue. In many instances the 

 direction of the internal fasciculi is horizontal, and that of the ex- 

 ternal, oblique, or more rarely longitudinal. 



There are no glands. 



In the oesophagus of the Frog the mucous membrane is lined with 

 ciliated epithelium, similar in thickness and form to that already de- 

 scribed in the Triton. In preparations hardened in alcohol, nothing 

 but cup- or goblet-shaped cells are to be found over tracts of con- 

 siderable extent. 



The mucous membrane is strongly developed ; its fasciculi pursue a 

 horizontal course parallel to one another from without inwards till 

 they reach the epithelium, beneath which, becoming bent at right 

 angles, they assume a plexiform arrangement. The portion in contact 

 with the external muscular layer, that is to say, the submucous tissue, 

 contains the larger vascular trunks in its meshes. 



The acinous glands in the Frog form an almost continuous layer 

 from 0*4 to 0'5 of a millimeter in thickness. The acini vary in size, 

 and are rounded or oval in form. They are lined by an epithelium 

 consisting of closely compressed, rounded, or flattened by mutual pres- 

 sure, cubical, or cylindrical cells. No muscularis mucosa3 exists in 

 the upper part, but in the lower there is to be found in patches situ- 

 ated externally to the glands a not very strong layer of longitudinal 

 smooth muscular fibres, from which, as well as from the circular layer 

 of the external muscular coat of the upper part, a few fasciculi are 

 given off, that penetrate between the glands. 



