44 



GENERAL ANATOMY. 



inclines to the columnar shape. It is distinguished by the presence of minute 

 processes, which are direct prolongations of the cell-protoplasm standing up from 

 the free surface like hairs or eyelashes (cilia). If the cells are examined during 

 life or immediately on removal from the living body (for which in the human sub- 

 ject the removal of a nasal polypus offers a convenient opportunity) in tepid 

 water, the cilia will be seen in lashing motion ; and if the cells are separate, they 

 will often be seen to be moved about in the field by that motion. 



The situations in which ciliated epithelium is found in the human body are : 

 the respiratory tract from the nose downward (except over the lower portion of the 

 pharynx and the surface of the vocal cords) the tympanum and Eustachian tube, 

 the Fallopian tube and upper portion of the uterus, the vasa efferentia, coni vas- 

 culosi, and first part of the excretory duct of the testicle, and the ventricles of the 

 brain and central canal of the spinal cord. 



Stratified epithelium consists of several layers of cells superimposed one on the 

 ^ top of the other and varying greatly in shape. The cells of the deepest layer are 



for the most part columnar in 

 form, and as a rule form a sin- 

 gle layer, placed vertically on 

 the supporting membrane ; above 

 these are several layers of sphe- 

 roidal cells, which as they ap- 

 proach the surface become more 

 and more compressed, until the 

 superficial layers are found to 

 consist of flattened scales, the 

 margins of which overlap one 

 another, so as to present an im- 

 bricated appearance. Another 

 form of stratified epithelium is 

 found in what has been termed 

 transitional epithelium, such as / 

 exists in the ureters and urinary 

 bladder. Here the cells of the 

 most superficial layer are cubical, 

 with depressions on their under 

 surfaces, which fit on to the 

 rounded ends of the cells of the 

 second layer, which are pear- 

 shaped, the apices touching the 



basement-membrane. Between their tapering points is a third variety of cells, 

 filling in the intervals between them, and of smaller size than those of the other 

 two layers. 



2. Endothelium. As before stated, endothelial cells are flattened, transparent, 

 squamous cells, attached by their margins by a semi-fluid homogeneous cement- 

 substance, so as to form a continuous endothelial membrane. Though for the most 

 part these cells are squamous, in some places cells may be found, either isolated 

 or occurring in patches, which are polyhedral or even columnar. These latter 

 cells are frequently to be found lining the stomata of serous membranes (Fig. 12). 

 As a rule, the endothelial cells are polygonal in outline, with sinuous or jagged 

 margins, and are in close apposition, the amount of cohesive matter uniting them 

 being so slight as not to be apparent. Their protoplasmic substance appears to be 

 granular, but consists of fibrillse arranged in a network in which the nucleus is 

 contained, limited by a membrane and having a well-developed reticulum. 



CONNECTIVE TISSUES. 



By the term connective tissue we mean a number of tissues which possess this 

 feature in common viz. that they serve the general purpose in the animal economy 



FIG. 12. Part of peritoneal surface of the central tendon of 

 diaphragm of rabbit, prepared with nitrate of silver, s. Stomata. 

 t. Lymph-channels, t. Tendon-bundles. The stomata are sur- 

 rounded by cubical endothelial cells. (From Hand-book for 

 the Physiological Laboratory, Klein.) 



