THE STRUCTURE OF THE ELEMENTARY TISSUES. 45 



nuchae of such animals as the ox and horse, in which that ligament is 

 largely developed (fig. 40). 



(c.) Elastic membranes with perforations, e.g., Henle's fenestrated 

 membrane : this variety is found chiefly in the arteries and veins. 



(d.) Continuous, homogenous elastic membranes, e.g., Bowman's an- 

 terior elastic lamina and Descemet's posterior elastic lamina, both in the 

 cornea. 



A certain number of flattened connective-tissue cells are found in 

 the ground substance between the elastic fibres which make up this 

 variety of connective tissue. 



(c.) Areolar Tissue. 



Distribution. This variety of fibrous tissue has a very wide distribu- 



Fig. 43. Fig. 44. 



Fig. 43. Transverse section of tendon from a cross section of the tail of a rabbit, showing 

 sheath, fibrous septa, and branched connective-tissue corpuscles. The spaces left white in the 

 drawing represent the tendinous fibres in transverse section. X <J50. (Klein.) 



Fig. 44. Transverse section of a portion of lig. nuchae, showing the outline of the fibres. (After 

 Stohr.) 



tion and constitutes the subcutaneous, subserous, and submucous tissue. 

 It is found in the mucous membranes, in the true skin, and in the outer 

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

 and the internal organs, and penetrating into their interior, 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. Under the microscope it is found to be made up of fine white 

 fibres, which interlace in a most irregular manner, together with a vari- 

 able number of elastic fibres. On the addition of acetic acid, the white 

 fibres swell up, and become gelatinous in appearance; but as the elastic 

 fibres resist the action .of the acid, they may still be seen arranged in 



