214 MANUAL OF HISTOLOGY. 



branches which subdivide again and again (Fig. 100) to form 

 loops or coils ; these latter unite again and form a vessel equal 

 in size to the one which entered the capsule. The first is 



called, as already described, the affer- 

 ent ; the second, the efferent vessel, 

 and the glomerulus is formed by the 

 division and reunion of the branches 

 of these two vessels ; the whole form- 

 ing a rounded tuft within the capsule. 

 The vessels of which a glomerulus is 

 composed have the same diameter as 

 FIG. loo. Giomeruius from kidney small capillaries i their coats are struc- 



of pig. Ludwig. ' . . . 



tureless and provided with elliptical 



nuclei. The efferent vessels are not veins ; on leaving the cap- 

 sules they break up into capillaries, which anastomose freely 

 with each other and surround the tubules of the cortex, form- 

 ing, in this way, a network with circular meshes (Fig. 99, D). 



At the boundary layer the capillaries unite to form vessels 

 which are two to three times larger than the original capillaries. 

 These vessels take a straight course through the medulla to- 

 ward the apices forming the so-called vasa recta ' (Figs. 99, E, 

 and 89, G). The vessels immediately below the boundary layer 

 are arranged in bundles at the side of the pyramidal prolonga- 

 tions, and run parallel with them in that part of the medulla 

 (Fig. 89). They give off branches in the medulla, and near the 

 apices of the pyramids again form a capillary network which 

 surrounds the collecting tubules. The returning vessels (veins) 

 have about the same course, anastomose freely with each other, 

 and empty into the venous arches at the boundary layer. 

 Other veins are formed by the union of capillaries immediately 

 underneath the capsule ; these have a stellate form, 3 the centre 

 of each star indicating the commencement of a vein. Such 

 veins, passing downward through the cortex and receiving 

 branches on the way, empty finally into the venous arches 

 above referred to. The venous arches also give rise to vessels 

 of larger calibre, which run parallel to and accompany the ar- 

 teries of the medulla, and at last unite to form the renal vein. 



Injections of the kidney. The kidney may be injected with 

 gelatine either through the artery or vein. It is best accom- 



1 Bonders: Physiol., L 2 Venae Stettatce, Verheyen. 



