THE BLOOD-VESSELS. 



153 



intima and the media marks the transition of a minute into a 



small artery. This new layer consists at lirst of delicate fibrils 



of elastic tissue, or an apparently homogeneous membrane. 



Vascular contraction throws it into folds, which appear as 



longitudinal striae or a transverse series of continuous festoons. 



As the vessel grows larger this coat gets thicker, becomes dis 



tinctly fenestrated, and presents a reticulat- 



ed appearance. It is now made up of inter- 



lacing bundles of connective tissue and elas- 



tic fibres, with spaces left between them. 



The latter constitute the fenestrse of this 



layer, which in the large vessels becomes a 



double or triple lamellated membrane. Be- 



tween it and the lining endothelium there 



appears still another structure, which has re- 



ceived various names from different authors. 



Thus, Kolliker has called it the striated in- 



ternal coat; Remak, the innermost longi- 



tudinal fibrous coat ; and Eberth, the in- 



ternal fibrous coat. We shall employ the 



last term. The internal fibrous coat consists 



at birth of a granular substance, which be- 



comes distinctly fibrillated in the adult. 



Embedded in this membrane lie numerous 



branching corpuscles, containing large, con- 



spicuous nuclei. Besides these cells, smaller, 



so-called granulation-bodies are frequently 



seen. So far from regarding them as of path- 



ological origin (Eberth, in " Strieker's His- 



tology"), I prefer to consider them as ma- 



trix-cells for the regeneration of desquamated 



i 4! i- \t f i 



endothelia. My reasons for so doing are , muscio nucleus ; c, 



/ 1 1 T j. i i i i i f internal tunic ; rf, membrane 



as lollows : In the blood-vessels of young formed of fusiform oeiu. 

 animals and newly born infants I have fre- 

 quently noticed thick, dark, and granular bodies immediately 

 below the endothelial lining. These subendothelial cell-plates 

 were smaller and more polyhedral than ordinary endothelia, 

 and invariably contained one or even two nuclei. They ap- 

 peared to resemble germinating endothelial cells, such as Klein 

 has described as occurring in serous membranes. They did 

 not, however, occur in single layers, as Klein has seen them, 



PIO. 67.-smaii artery 

 unTd^ vet"tia! ?x.'nu'- 



clei of the tunica ad ventitia; 



