CHAP. XXVIII.] 



CAPILLARY VESSELS. 



329 



are very remote from a large portion of the constituent osseous 

 particles; ramifying through Haversian canals, they come in contact 



Fig. 195. 



A. A capillary vessel from,the vesicular matter of the human brain, a. Homogeneous wall. 

 A. Nucleus of the wall. Red "blood-corpuscle. 



B, C. Different appearances of small arteries and veins of the human pia- mater. , a. Ho- 

 mogeneous membrane, b, b. Circular fibres, c, c. Oval nuclei of the internal epithelium, 

 here about to cease, d, d, Transverse indications of the circular fibres. 



D. Capillary arteiy from the mesentery of a rabbit. Magnified 200 diameters. 



only with the osseous particles of those layers which immediately 

 invest each canal; or with the periosteal or medullary layers. Vessels 

 do not penetrate articular cartilage at all, which must therefore draw 

 its nourishment from the vessels of neighbouring tissues. 



The finest capillaries, such as may be most easily examined in 

 connexion with the pia-matter of the brain, appear to consist of a 

 homogeneous tissue, interrupted at short intervals by nuclei, which 

 adhere to, or are embedded in, the wall of the vessel. (Fig. 195 A). 

 These nuclei are mostly oval sometimes nearly circular; most of 

 them have their long axes directed parallel to the course of the 

 vessel, but some are placed transversely. In some of these fine 

 capillaries, very faint indications of a circular striation may be seen. 



In some larger vessels, which, perhaps, may with more propriety 

 be regarded as capillary arteries, rather than as true capillaries, a 

 distinct arrangement of circular fibres may be seen. These fibres 

 are flat, uniform in diameter, devoid of nuclei, and in all respects, 

 but this, resemble the unstriped muscular fibres. 



It had long been a question among physiologists, whether the 

 capillaries had proper walls distinct from the tissues to which they 



VOL. II. Z 



