CILIATED EPITHELIUM. 203 



varicose filament ; these filaments are termed by Engelmann the rootlets of the cilia. 

 They approach one another as they traverse the length of the cell, and may be 

 united towards the extremity into a single thread. They are not connected with 

 the nucleus. The cilia are attached to the basal knobs, each one by a somewhat 

 narrowed portion or neck (intermediate segment of Engelmann). It is here 

 that the cilia usually break off from the cell (see fig. 238). Beyond the neck 

 the cilium swells out into a small bulbous enlargement, and from this the shaft 

 tapers gradually to its extremity. The rootlets, as well as the cilia themselves, are 

 said by Engelmann to be doubly refracting (anisotropous), whereas the basal knob 



Fig. 237. CILIATED EPITHELIUM CELLS FROM THE 



TRACHEA OF THE RABBIT J HIGHLT MAGNIFIED 

 (E. A. S.). 



TO 1 , m 2 , m 3 , mucus-secreting cells, lying between 

 the ciliated cells, and seen in various stages of 

 mucin-formation. 



is isotropous. A similar structure, although 

 less distinct, is also to be made out in 

 ciliated cells from higher animals (frog and 

 mammal). 



The columnar ciliated epithelium may 

 exist as a simple layer, as in the uterus and 

 Fallopian tubes, the finest ramifications 



.. Fig. 238. A CILIATED EPITHELIUM-CELL 



of the bronchia, and the central canal OF A MOLLUSK. (Engelmann.) 



of the spinal cord and ventricles of the 

 brain ; but in various other parts as the 



nose, pharynx, Eustachian tube, the trachea and its larger divisions there is a 

 layer of elongated and irregular cells beneath the superficial ciliated range, filling 

 up the spaces between the pointed and forked extremities of the latter. These cells 

 have been supposed to acquire cilia, and take the place of ciliated cells which 

 are cast off ; but this is doubtful, and they appear rather to be concerned with 

 the secretion of mucus, since mucigen occurs within them in all stages of formation, 

 and they become eventually distended by it into goblet-cells (see fig. 237, where the 

 intermediate cells, m 1 , m 2 , and m? show three stages of formation of mucus). 



When the ciliated epithelium is artificially removed from a portion of the inner surface of 

 the rabbit's trachea, the denuded surface speedily becomes again covered with epithelium, 

 which grows over it from the edge, but the cells form at first a single layer of flattened 

 epithelium. They next acquire cilia, and afterwards become columnar, the epithelium thus 

 assuming the character which it has normally in that situation. 



VOL. i. p 



