STRUCTURE OF THE ELEMENTARY TISSUES. 



31 



Fro. 28. Elastic fibres from the 

 ligamentasubflava. x 200. (Shar- 



from white fibres by the following characters: (1.) Their great power of 

 resistance even to the prolonged action of chemical reagents, e.g., Caustic 

 Soda, Acetic Acid, etc. (2.) Their well-de- 

 iined outlines/ (3.) Their great tendency to 

 branch and form networks by anastomosis. (4. ) 

 They very often have a twisted corkscrew- 

 like appearance, and their free ends usually 

 curl up. (5.) They are of a yellowish tint 

 and very elastic. 



VARIETIES OF CONNECTIVE TISSUE. 

 I. FIBROUS CONNECTIVE TISSUES. 



A. Chief Forms. (a.) Areolar Tissue. 



Distribution. This variety has a very wide 

 distribution, and constitutes the subcutaneous, 

 subserous and submucous tissue. It is found 

 in the mucous membranes, in the true skin, in pej-) 

 the outer sheaths of the blood-vessels. It forms sheaths for muscles, 

 nerves, glands, and the internal organs, and, penetrating into their in- 

 terior, supports and connects the finest parts. 



Structure. To the naked eye it appears, when stretched out, as a 

 fleecy, white, and soft meshwork of fine fibrils, with here and there wider 

 films joining in it, the whole tissue being evidently elastic. The open- 

 ness of the meshwork varies with the locality from which the specimen is 

 taken. On the addition of acetic acid the tissue swells up, and becomes 

 gelatinous in appearance. Under the microscope it is found to be made 

 up of fine white fibres, which interlace in a most irregular manner, to- 

 gether with a variable number of elastic fibres. These latter resist the 

 action of acetic acid as above mentioned, so that when this reagent is 

 added to a specimen of areolar tissue, although the white fibres swell up 

 and become homogeneous, certain elastic fibres may still be seen arranged 

 in various directions, sometimes even appearing to pass in a more or less 

 circular or in a spiral manner round a small mass of the gelatinous mass 

 of changed white fibres. The cells of the tissue are arranged in no very 

 regular manner, being contained in the spaces (areolse) between the fibres. 

 They communicate, however, with one another by their branched pro- 

 cesses, and also apparently with the cells forming the walls of the capil- 

 lary blood-vessels in their neighborhood, connecting together the fibrils 

 in a certain amount of albuminous cement substance. 



(b.) White Fibrous Tissue. 



Distribution. Typically in tendon; in ligaments, in the periosteum 

 and perichondrium, the dura mater, the pericardium, the sclerotic coat 



