464 
DE. HEEBEET WATNEY ON THE MINUTE 
From what has been explained before of the relation of the connective-tissue reti- 
culum to the individual muscle-fibres, it will be easy to understand that the reticulum 
surrounding the bundle of fibres is attached to the reticulum of the mucosa, each fibre 
having here, as in the colon, its own ending : if the fibres end near the membrana, they 
may be apparently attached to the large cells composing it. 
Structure and delations of the Blood-vessels of the Mucosa. 
These vessels have an adventitia — that is to say, in sections showing the longitudinal 
course of the vessel, threads are seen attaching the vessel to the reticulum of the mucosa 
(see Plate 40. figs. 15, 17, and 18). There is, however, considerable difference in the 
arrangement of this adventitia as regards the arteries and veins. 
First, as regards the arteries. In those places where the minute arteries have a 
distinct and continuous layer of involuntary muscle-fibres*, as in the commencement of 
the duodenum in some animals ( i . e. in the dog, rat, and hedgehog), the reticulum passes 
between and surrounds the involuntary muscle-fibres (see fig. 15). Whether the reti- 
culum penetrates between the endothelial plates of the artery, I have been unable to 
discover. 
In other parts of the mucosa we find arteries without a continuous layer of muscle- 
fibres — that is to say, the muscles are situated at some distance from one another; where 
that is the case, the reticulum surrounds the vessel much as it does in the former case 
(compare figs. 16 & 15). 
A somewhat similar appearance to that in fig. 16 would no doubt be given by a 
longitudinal section of an artery in which the muscle-fibres were situated principally 
above or below the vessel, as in such a section most of the fibres would be cut near their 
ends ; the fibres would then look like clear rings, and would show no trace of nucleus. 
That this explanation is, however, not suitable is proved by sections which are thick 
enough to show the whole vessel : by focusing up and down in these sections, we can 
assure ourselves that there is no continuous layer of involuntary muscle-fibres surrounding 
the artery, and that there are only a few fibres at rare intervals ; and in such a prepa- 
ration, on accurately focusing the lumen of the vessel, we obtain an appearance similar 
to fig. 16. 
In the minute arteries of many villi there are no involuntary muscle-fibres at all ; we 
shall, however, often be able to recognize the arterial character of these vessels by the 
marked adventitia. 
Secondly, as regards the relations of the adventitia to the veins. 
In the veins the adventitia is not so distinctly seen as a separate membrane ; it can, 
however, be shown to exist, and an adventitia is present here in the same sense that an 
adventitia may be said to surround the involuntary muscle-fibres. See fig. 18, where 
in places the reticulum surrounding the vessel is seen, and compare figs. 17 & 18. 
* Donders (12) noticed ring-shaped nuclei around the arteries in the villi. 
