Physiology of the Motor Apparatus. 



291. [CILIARY MOTION PIGMENT CELLS]. [(a) Muscular Move- 

 ment.- By far the greatest number of the movements occurring in our bodies is 

 accomplished through the agency of muscular fibre, which, when it is excited by a 

 stimulus, contracts, i.e., it forcibly shortens, and thus brings its two ends nearer 

 together, while it bulges to a corresponding extent laterally. In muscle, the con- 

 traction takes place in a definite direction.] 



[(b) Amoeboid Movement. Motion is also exhibited by colourless blood-cor- 

 puscles, lymph-corpuscles, leucocytes, and some other corpuscles. In these 

 structures we have examples of amoeboid movement ( 9), which is movement in 

 an indefinite direction.] 



[(c) Ciliary Movement. There is also a peculiar form of movement, known as 

 ciliary movement. There is a gradual transition between these different forms of 

 movement. The cilia which are attached to the ciliated epithelium are the motor 

 agents (fig. 300).] 



[Ciliated epithelium where found. In the nasal mucous membrane, except the olfactory 

 region ; the cavities accessory to the nose ; the upper half of the pharynx, Eustachian tube, 

 larynx, trachea, and bronchi ; in the uterus, 

 except the lower half of the cervix ; Fallopian 

 tubes ; vasa efFerentia to the lower end of epi- 

 didymis ; ventricles of brain (child) ; and the 

 central canal of the spinal cord.] 



[The cilia are flattened blade-like or hair-like 

 appendages attached to the free end of the 

 cells. They are about ^Vir inch in length, and 

 are apparently homogeneous and structureless. 

 They are planted upon a clear non-contractile 

 disc on the free end of the cell, and some oh- , t ^^^P^^^^^^^P"" - layer 



servers state that they pass through the disc to ^ v ^s " ^^^^^^S^^^ 



become continuous with the protoplasm of the l ' 



cell, or with the plexus of fibrils which pervades S* 



the protoplasm, so that by some observers they Ciliated epithelium, 



are regarded as prolongations of the intra-epi- 



thelial plexus of fibrils. They are specially modified parts of an epithelial cell, and are con- 

 tractile and elastic. They are colourless, tolerably strong, not coloured by staining reagents, 

 and are possessed of considerable rigidity and flexibility. They are always connected with the 

 protoplasm of cells, and are never outgrowths of the solid cell membranes. There may be 10 

 to 20 cilia distributed uniformly on the free surface of a cell (fig. 300).] 



[In the large ciliated cells in the intestine of some molluscs (mussel), the cilia perforate the 

 clear refractile disc, which appears to consist of small globules basal pieces united by their 

 edge, so that a cilium seems to spring from each of these, while continued downwards into the 

 protoplasm of the cell, but not attached to the nucleus, there is a single varicose fibril rootlet, 

 and the leash of these fibrils passes through the substance of the cell and may unite towards its 

 lower tailed extremity (Engdmann).] 



[Ciliary motion may be studied in the gill of a mussel, a small part of the gill being teased 



