THE MAST CELLS 



the imprint of connective tissue fibrils — clear lines across the cytoplasm which 

 were regarded as 'granule canals' (Lehner, 1924) until their true nature was 

 established by Webb (1931-32). These isolated clumps are characteristic of 

 the dorsal connective tissue and are not seen elsewhere. 



In the flanks near the mammary glands, portions of which were sometimes 

 included in the spreads, the Y-shaped vessels with double muscle coats undergo 

 repeated bifurcation to become capillaries. Here the difference in distribution 

 of the two types of mast cells is very striking (Fig. 11). In the adventitia of 

 the muscular vessels pure type-I mast cells are often arranged in unbroken 



"«• 





j0^&pmmm 



rtf 







1 



»V 



Fringe of arborising vascular pattern in subcutaneous connective tissue. The associated mast cells 



are mainly type II and as they migrate away from the vessels they become smaller from loss of 



granule substance ( 55). (Riley (1953), J. Path. Bad. 65, 461.) 



chains; these gradually change into type-II cells and clumps as the capillaries 

 appear. 



Mesentery 



Vessels. The mesenteric vessels in the rat, as in man, form vascular arcades 

 framing clear peritoneal windows. In the rat these arcades usually consist of 

 more than one pair of muscular vessels enclosed in a common sheath of fat. 

 At intervals, lateral twigs from the muscular vessels pierce the fat and ramify 

 as a delicate lacework of capillaries over the peritoneal window. 



52 



