CH. LVIII.] LAYERS OF THE BLASTODERM. 815 



d. The epithelium of the mouth, the enamel of the teeth. 



e. The epithelium of the nasal passages. 



/. The epithelium of the glands opening on the skin and into 

 the mouth, and nasal passages. 



g. The muscular fibres of the sweat-glands. 



2. From Mesoblast. a. The skeleton and all the connective- 

 tissues of the body. 



b. All the muscles of the body except those of the sweat- 

 glands. 



c. The vascular system, including the lymphatics, serous mem- 

 branes, and spleen. 



d. The urinary and generative organs, except the epithelium of 

 the bladder and urethra. 



The Somatopleur forms the osseous, fibrous, and muscular tissues 

 of the body-wall including the true skin. 



The Splanchnopleur forms the fibrous and muscular walls of 

 the alimentary canal, the vascular system, and the urino-genital 

 organs. 



3. From Hypoblast. a. The epithelium of the alimentary 

 canal from the back of the mouth to the anus, and that of all the 

 glands which open into this part of the alimentary tube. 



b. The epithelium of the respiratory cavity. 



c. The epithelium of the Eustachian tube and tympanum. 



d. The epithelium lining the vesicles of the thyroid. 



e. The epithelial nests of the thymus. 



/. The epithelium of the bladder and urethra. 



The Foetal Membranes. 



This subject will be best understood by taking a view (fig. 630) 

 of the uterus and its contents after the formation of all the 

 membranes. We can then pass to the way in which the several 

 membranes are formed. 



The uterus, the muscular walls of which are hypertrophied, is 

 lined by a greatly thickened mucous membrane, which is called 

 the decidua, because after the delivery of the child it comes away 

 from the uterus with the other membranes. The decidua is 

 divided into three parts ; the lining of the uterine cavity is 

 called the decidua vera (dv) ; a continuation of this reflected over 

 the foetus and its membranes is called the decidua reftexa (dr) ; 

 the portion of the decidua vera which is situated within the line 

 of attachment of the decidua reflexa is called the decidua 

 serotina (dt). These membranes are matemal in origin. Within 

 the decidua reflexa are situated the foetal membranes ; the outer- 



