210 FRANKLIN PARADISE JOHNSON 



epithelium up into an irregular network such as Langer ('87) 

 has described in connection with the developing colic valve. 

 The clefts in between the ridges are deep, and into them open 

 the lumina of the intestinal glands. An examination of the 

 basal surface of another model (not figured), from the same por- 

 tion of the large intestine, shows numerous tubular glands, many 

 of which are unbranched, but the branched type is not uncommon. 

 As stated before, the first beginnings of the intestinal glands 

 appear as small knob-like processes which extend into the under- 

 lying mesenchyma. At the time they appear no muscularis 

 mucosae is present. In embryos of 99 mm., 110 mm., 14Q mm., 

 the muscularis mucosae is still not visible; nevertheless, the 

 intestinal glands all reach a certain depth, so that in a section, 

 a line drawn parallel to the surface of the mucous membrane 

 would practically touch the bottoms of all the glands. It is 

 along this line, or rather, slightly below it, that the muscularis 

 mucosae is becoming visible in an embryo of 187 mm. It is 

 seen as a slight condensation of the mesenchyma forming a cir- 

 cular band of about 0.014 mm. in thickness. In it are observa- 

 ble, though not very distinctly, developing myoblasts. The 

 band is slightly more distinct at 190 mm., and separates the 

 connective tissue of the submucosa, which is condensed and 

 well stained, from that of the tunica propria, which is loosely 

 arranged and only faintly or not at all stained. At 187 and 

 190 mm. the basal ends of the glands can be seen resting upon 

 this layer of muscle. 



Further formation of glands 



As the glands are gradually increasing in number as the growth 

 of the embryo proceeds, the question arises, how are new glands 

 formed? Do they develop like new villi, by evaginations of 

 the epithelium between those already formed, or are they devel- 

 oped after the manner which Patzelt has described, by a longi- 

 tudinal splitting of those already present? In his discussion of 

 this point Patzelt says: 



