THE CELL AND THE TISSUES. 2$ 



Derivatives of the Primary Blastodermic Layers. 



From the ectoderm are derived 



The epithelium of the outer surface of the body, including that 

 of the conjunctiva and anterior surface of the cornea, the 

 external auditory canal, together with the epithelial append- 

 ages of the skin, as hair, nails, sebaceous and sweat glands 

 (including the involuntary muscle of the latter). 



The epithelium of the nasal tract, with its glands, as well as of 

 the cavities communicating therewith. 



The epithelium of the mouth and of the salivary and other 

 glands opening into the oral cavity. 



The enamel of the teeth. 



The tissues of the nervous system. 



The retina; the crystalline lens. 



The epithelium of the membranous labyrinth. 



The epithelium of the pituitary and pineal bodies. 



From the mesoderm are derived 



The connective tissues, including areolar tissue, tendon, cartilage, 



bone, dentine of the teeth. 

 The muscular tissues, with the exception of the muscle of the 



sweat-glands. 

 The tissues of the vascular and lymphatic systems, including 



their endothelium and circulating cells. 

 The sexual glands and their excretory passages, as far as the 



termination of the ejaculatory ducts and vagina. 

 The kidney and ureter (but not the bladder). 



From the entoderm are derived 



The epithelium of the digestive tract, with that of all glandular 



appendages except those portions derived from ectodermic 



origin at the beginning (oral cavity) and termination of the 



tube. 



The epithelium of the respiratory tract. 

 The epithelium of the urinary bladder and urethra. 

 The epithelium of the thyroid and thymus bodies, the atrophic 



primary epithelium of the latter being represented by Hassall's 



corpuscles. 



