g6 ninth lecture. 



the conjunction of the branches there are formed reticula 

 of more regular, and frequently of extremely characteristic 

 form. 



The diameter of the capillaries (see above) is by no means 

 the same in the different portions of the human body. The 

 brain and retina present the finest of 0. 0068 to 0.0065 mm., 

 and less. The muscles have somewhat larger ones of 0.0074 

 mm. The calibre is again increased, somewhat, in those of 

 the connective tissue, the external integument, and the mu- 

 cous membranes. The lumen is greater in the capillaries of 

 most of the glands, such as the liver, the kidneys, and the 

 lungs. Here we have a diameter of 0.0099 to 0.0135 mm. 

 The most considerable ones, finally, of 0.0226 mm., are seen 

 in the bone medulla. That, with the larger blood corpuscles, 

 even the finest capillaries of animals have a more considerable 

 calibre, it is hardly necessary to remark. 



The capillaries are sometimes more profuse, sometimes more 

 scanty, in a part of the body. The size of the portion of the 

 tissue comprised within their net-work is, accordingly, quite 

 variable ; it is small in the vascular, large in the non-vascular 

 parts. The former have an energetic, the latter a sluggish 

 assimilation. The lungs (Fig. 92) appear uncommonly vas- 

 cular. Their capillary net- work,- serving for respiration, is the 

 most compact of the organism. The other glands approxi- 

 mate. The fibrous membranes, the tendons, the neurilemma 

 are quite non-vascular. 



The form of the capillary net-work is determined by the 

 shape of the parts to be circumvoluted, the nature of the 

 several elements, or of their arrangement. 



We have, firstly, the straight, capillary net-work. A trans- 

 versely striated muscle (Fig. 91) may represent this. The 

 several filaments are surrounded by the uncommonly elongated 

 meshes (c). The involuntary, smooth muscles also possess 

 the same capillary net-work. Here, however, from the thin- 

 ness of the elements, a bundle of fibres takes the place of 

 the transversely striated filament. 



Other parts with elongated elements — for example, the gas- 



