GENERAL EMBRYOLOGY 1617 



Structures derived from the Germinal Layers. 



Eetoderm. 



1. The nervous s\^tem — ^that is to say, the spinal cord and 

 enceptialon, the peripheral nen-es, and the s}Tnpathetic s\-stem. 



2. The epithelial elements of the organs of sense, except the 

 tongue — e.g., the epithelial elements of the olfactory region, internal 

 ear, optic nerve, and retina. 



3. The epithelial elements of the posterior lobe of the pituitary 

 body, and those of the pineal body. 



4. The cr\-stalline lens. 



5. The epidermis and its appendages — e.g., the hairs and nails. 



6. The epithelial elements of the sebaceous glands, sweat-glands, 

 and mammary glands. 



7. The plain muscular tissue connected with the hair-follicles, 

 and arranged as the musculi arrectores pilorum, as well as the plain 

 muscular tissue of the sweat-glands. 



8. The epithelium of the roof and sides of the mouth, but not that 

 which covers the tongue and back part of the floor of the mouth ; 

 the epithehum of the salivary' glands ; the enamel of the teeth ; and 

 the anterior lobe of the pituitar\' bod\-. 



9. The epithelium of the nasal fossae and of the air-sinuses which 

 communicate \viih them, as well as of the naso-phar\"nx. 



10. The epithehum of the external auditory meatus and outer 

 layer of the membrana t^-mpani. 



11. The epithehum of the conjunctiva and front part of the 

 cornea. 



12. The epithelium (modified epidermis) of the anal canal below 

 the anal valves. 



13. The epithelium of the spongy part of the male urethra. 



Entoderm. 



1. The epithehum of the alimentar\' canal, except the following 

 parts: (a) The re of and sides of the mouth; (6) the naso-pharynx ; 

 and (c) the anal canal below the anal valves. 



2. The epithehum of the tongue (including that of the taste-buds) 

 and of the back part of the floor of the mouth. 



3. The epithelium of the glands which open into the alimentary 

 canal (except the sahvary glands) — e.g., the hver and pancreas. 

 The epithehmn of the gall-bladder is included. 



4. The epithelium of the Eustachian tube and t\Tnpanum. 



5. The epithelium of the th\Toid and thymus bodies. 



6. The epithelium of the respirator^' tract — e.g., the lar5aix, 

 trachea, bronchial tubes, and air-cells of the lungs. 



7. The epithehum of the urinary* bladder, of the prostatic and 

 membranous parts of the male urethra, and of the whole of the 

 female urethra. 



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