EPITHELIAL TISSUES 



19 



subdivide it into three or four segments, in the center of which 

 is the nucleus. They are probably exoplasmic derivatives of the 

 cell protoplasm. Similar fibrils, though less pronounced, have 

 also been found in other tissues than epithelium i. e., in smooth 

 muscle and in nerve cells. 



CLASSIFICATION OF EPITHELIA 



I. SIMPLE EPITHELIA those which occur en masse, or composing a mem- 

 brane but one cell in thickness. 



Ovum. 



(d) Spherical cells. 



Graafian 



1. Spheroidal, composed of. 



2. Bquamous, composed of flat- 

 tened, scaly cells. 



Embryonal cells. 

 f Liver cells. 



(b) Polyhedral cells, -j Deeper layers of com- 

 [ plex epithelium. 

 ' Serous membranes, 

 synovial membranes, 

 bursse, and tendon 

 sheaths; heart, arter- 

 ies, capillaries, veins, 



closed 



(a) Lining 

 cavities. 



Pavement epitheli- 

 um or, endothe- 

 lium. 



and 



sels. 



lymphatic ves- 



3. Columnar. 



(b) Lining the alveoli of the lungs, some tu- 

 bules of the kidney, the anterior chamber 

 of the eye, and the membranes of the mid- 

 dle and internal ear. 



(c) As the superficial cells of stratified epithe- 

 lium (vide infra). 



(a) Lining the mucous membrane of the ali- 

 mentary tract stomach, small intestines, 

 large intestines. 



(b) Lining the ducts of all secreting glands 

 liver, pancreas, salivary, lachrymal, and 

 mammary glands, testicle, prostate, etc. 



(c) The deejpest layer of cells in stratified epi- 

 thelium is composed of columnar-shaped 

 cells, which, however, differ in structure 

 from the true columnar type. 



(a) Lining the uterus and Fallopian tubes. 



(b) Lining portions of the ventricles of the 

 brain and central spinal canal of the em- 



l bryo and infant, f 

 (O Pyramidal or [ The secreting cells of all tubular glands- 



\ / J \7if\rm\T lt > i , . !, 1.1 L: caliirat*\r nrionHc r>wr\TG f\T 



(A) Simple 



() Ciliated, 



glandular." 



(D) Goblet, 



(E) Neuro-epithe- 

 lium. 



j kidney, pancreas, salivary glands, crypts of 

 [ the intestines, etc. 



{(a) Respiratory tract nasal, pharyngeal, tra- 

 cheal. and bronchial mucous membranes. 

 (b) Alimentary tract stomach, small and 

 large intestines. 



f (a) Eye the rod and cone cells of the retina. 

 I (6) Ear in the maculse of the labyrinth and 



Iin Corti's organ. 

 (c) Nose in the olfactory mucous membrane. 

 (d) Tongue in the taste buds. 



