I.] THE FROG. 149 



contour line. Look for places where it may 

 have been separated in preparation. 



ft. Longitudinal muscular layer ; thin and deeply 

 stained ; seen to consist of the cut ends of 

 close-set cells. 



y. Circular muscular layer; relatively thicker 

 than ft; cells close-set and parallel with the 

 free surface (cf. 7. b. ft). 



S Submucous layer ; faint and composed of vas- 

 cular connective tissue. Large blood-vessels 

 will be seen ramifying within it. 



. Mucous membrane; composed of three layers. 

 A muscular layer, forming a thin stratum im- 

 mediately internal to 8; a lymphoidal layer, 

 somewhat like the submucous layer, but con- 

 taining numerous rounded or irregular cells 

 (lymphoidal cells) ; the epithelium, composed 

 of close-set columnar cells (cf. 2. b.} whose 

 inner ends for the most part stain very deeply. 



c. Compare similar sections across an intestine the 

 blood-vessels of which have been injected with 

 gelatine (see Appendix C). Note the course 

 of the vessels, and especially the relations of 

 their ultimate ramifications. 



17. The pancreas. 



Preserve small portions in alcohol of increasing 

 strengths ; stain with borax-carmine ; imbed and cut 

 transverse sections ; mount in Canada balsam. 



a. Examine under a low power. 



a. '\\izgland; composed of groups of cells (acini) 



