VARIOUS MEMBRANES AND TISSUES. 121 



for instance, which is very elastic in order to allow of any sudden expan- 

 sion of the part, is principally composed of it. 



235. Areolar tissue. 



Areolar tissue consists of threads of white and yellow tissue woven 

 inextricably together. It is generated in cells, which elongate and join 

 in lines. It is but very slightly vascular, though many blood-vessels pass 

 through it en route to the skin. Its toughness and elasticity are admir- 

 ably proportioned to the mobility of each part. 



Areolar tisue is the most universal of the constituents of the body. 

 Under the name of superficial fascia, it spreads under the skin and ties 

 it down to the deeper parts, and it also forms a nidus for fat. It sepa- 

 rates and yet connects muscles and other parts. Hence it is also called 

 conjunctival or connective tissue. As parenchyma, it constitutes the 

 matrix of the most solid organs, and it forms pads for the protection of 

 and smooth capsules for the motion of such organs as the eye. 



The spaces or areolse, of which it consists, communicate freely with 

 each other. Hence it permits the transmission of air as seen in cases of 

 emphysema, or serum as in cases of anasarca, or blood as in ecchymosis, 

 and other fluids also over a great extent of space. Areolar tissue is some- 

 times called cellular membrane. 



236. Fascia. 



Fascia is a tendinous expansion, and differs from a tendon only in 

 that the fibres in the latter are in a collected form. 



237. Muscle. 



Muscle or Muscular tissue is what is ordinarily called flesh. It consti- 

 tutes the chief bulk of the soft external parts of the frame. 



Muscle is of two kinds, namely Voluntary and Involuntary. The 

 muscles of organic life, such as those of the digestive tract, the trachea, 

 bronchi, bladder, urethra, &c., belong to the Involuntary class. They 

 are not so red in colour or so large as the voluntary muscles, nor are they 

 attached to bones. They are further distinguished by being " unstriped," 

 that is, they have not the striped appearance which marks the voluntary 

 class. The Voluntary muscles move all those parts which are under the 

 control of the will. They are larger and redder than the involuntary 

 muscles, and present a striped appearance. 



Muscles consist of fibres, which are collected into bundles and are con- 

 nected together by areolar tissue. Each fibre may be divided lengthwise 

 into fibrillae. Each fibrilla is made up of a number of square or slightly 

 rounded cells arranged like a string of beads. Each fibre is clothed with 

 a fine transparent sheath called myolemma, and it ends abruptly in a 

 tendinous thread. In the Voluntary class the fibres generally run the 

 whole length of the muscle. 



Besides the voluntary and involuntary muscles, there is also another 



