54 



STUDENTS HISTOLOGY 



Ectoderm 



or 

 Epiblast 



EMBRYONIC DERIVATION OP TISSUES 



In correlating the work of histology with that of embryology, 

 the student will find the following table serviceable. The table 

 indicates from which layer of the blastoderm each of the prin- 

 cipal tissues is derived: 



The epithelium of the skin and all its appendages and glands. 



The epithelium covering the front of the eye, the crystalline lens, 

 and the retina. 



The epithelium of the external auditory canal and of the mem- 

 braneous labyrinth. 



The epithelium of the nasal cavity and its diverticula. 



The epithelium of the mouth and its glands, the salivary glands, 

 and the enamel of the teeth. 



The epithelium of the anal end of the alimentary canal. 



The tissues of the nervous system, the lining of the central canal 

 of the spinal cord and of the cerebral ventricles, the pituitary 

 and pineal bodies. 



All connective tissues. 

 Muscular tissue. 



The blood- and lymph-vessels and their endothelium, and the endo- 

 Mesoderm thelium of the serous membranes. 



or < Blood -and lymph-'corpuscles. 

 Mesollast The spleen and lymph -nodes. 

 The kidney and ureter. 



The ovary and testicle and their ducts, except the external ends of 

 the ducts. 



The epithelium of the alimentary canal (except at the upper and 

 lower extremities), and all the glands opening into it, includ- 

 Entoderm ing the liver, pancreas, thyroid, and thymus. 



or -s The epithelium of the respiratory tract which originates as a 

 Jlypoblast diverticulum from the alimentary canal. 



The epithelium of the Eustachian tube and tympanum. 

 The epithelium of the urinary bladder and urethra. 



EPITHELIUM 



Epithelium is the tissue covering the surfaces of the body that 

 V/ communicate with the external world, and lining the glands.* It 

 is made of cells, held together by only a small amount of 

 intercellular substance. 



*Note the exceptions in the case of the peritoneum, which is lined by endothelium, and which 

 opens externally by means of the Fallopian tube; the thymus and thyroid glands, and the 

 cavity of the central nervous system, which contain or are lined by epithelium, but do not open 

 externally. 



