EXAMINATION OF THE EYE. 671 



very irregular cells, folded over each other, and perhaps creased 

 in different directions. The epithelial cells of the mouth have 

 very distinct nuclei, which are m'ade to disappear under the 

 action of acetic acid. 



Tessellated or pavement epithelium is "beautifully shown in the 

 epidermis of the frog. It may be examined upon the choroid 

 coat of the eye, the lining membrane of the heart, arteries, veins, 

 and pelvis of the kidney, arid upon serous surfaces generally. 



Glandular or spheroidal epithelium consists of round cells, 

 which occasionally become polyhedral from mutual pressure. 

 The nucleus is usually well marked, and sometimes seems to be 

 surrounded with numerous minute granules and oil-globules. 

 This variety of epithelium is well shown in the sweat-glands, in 

 the convoluted tubes of the kidney, in the follicles of the sto- 

 mach, pancreas, liver, &c. 



Columnar, prismatic, or cylindrical epithelium, may be obtained 

 from the gall-bladder, the ureters, the urethra, the intestinal 

 villi, and the follicles of Lieberkiihn. 



Ciliated epithelium is found in the human body in the follow- 

 ing situations : On the surface of the ventricles of the brain, 

 and on the choroid plexuses ; on the mucous membrane of the 

 nose and its sinuses ; on the upper and posterior part of the soft 

 palate, and in the Eustachian tube ; in the cavity of the tympa- 

 num ; on the membrane lining the frontal and sphenoidal sinuses ; 

 on the inner surface of the lachrymal sac and lachrymal canal ; 

 on the mucous membrane of the larynx, trachea, and bronchial 

 tubes ; upon the os uteri ; within the cavity of the uterus ; through- 

 out the whole length of the Fallopian tubes, and upon their fim- 

 briated extremities (Beale). 



For examination, this variety of epithelium may be obtained 

 from the back part of a frog's mouth, or from the branchiae of 

 an oyster or mussel. 



EXAMINATION OF THE EYE. 



The cornea is examined by dividing the ball transversely with 

 a sharp knife, washing the anterior half, and removing the ciliary 

 processes. It is then pinned out flat and allowed to dry ; thin 

 sections are next made with very fine scissors ; these sections are 

 moistened with water, and finally treated with acetic acid, in 

 order to render the structures distinct. 



The elements composing the retina are most satisfactorily 

 examined in microscopic sections made at right angles to the 

 surface of the membrane, after maceration in dilute solution of 

 chromic acid. Viewed in this manner, according to Prof. Good- 

 sir, it exhibits from the peripheral to the central margin of a 

 successful section a series of strata, which may be distinguished 

 as the bacillary, white cellular, gray cellular, filamentary, and 

 limitary layers. 



