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



diminish in proportion as that increases, so that where the 

 muscular tissue attains its greatest thickness only a very few 

 small striae of connective tissue lie on its outer surface. 



At the commencement of this region, as in the intermediate 

 portion, the muscular tunic may be divided into two layers, an 

 internal longitudinal, and an external circular layer. 



In their further course the former, which constantly receives 

 fresh accessions of oblique fibres from the mucous membrane; 

 becomes first oblique and then circular. The external circular 

 layer is likewise strengthened by numerous fasciculi, originally 

 extending obliquely from without inwards, and arising from 

 the horny layer limiting the muscular tunic externally. A 

 considerable number of vessels and nerves run in the investing 

 sheath of connective tissue. 



After the remarks that have been already made respecting the 

 passage of the oesophagus into the stomach of the FROG, little 

 remains to be said in regard to the latter. The columnar epi- 

 thelium of the surface, which, after treatment with chromic 

 acid, is here likewise almost exclusively composed of well- 

 defined cup cells, the individual cells of which exhibit at their 

 attached extremity a longer or shorter cell process, continues 

 without interruption into the closely approximated tubes of 

 the mucosa. The cells lining the bottom of the tubes are 

 spheroidal and finely granular. 



The ciliated epithelium of the oesophagus does not entirely 

 cease at the cardia, but is here and there prolonged for some 

 distance ; and even at a much lower level individual ciliated 

 cells may occasionally be met with amongst the non-ciliated. 

 The tubes, which are coiled or lobulated at their extremities, 

 partly open by separate orifices, partly unite by twos in 

 cylindrical pits which, as above mentioned, are lined by cylinder 

 epithelium. 



The muscularis mueosse consists of an internal thinner cir- 

 cular and an external thicker longitudinal layer, the distinction 

 between which is only clearly marked in the lower half of the 

 stomach, whilst in the upper portion the fasciculi of the mus- 

 cularis mucosae are almost entirely longitudinal, or decussate to 

 some extent with one another. Everywhere small fasciculi are 

 given off, which penetrate between the tubes into the mucosa. 



