112 FRANCIS DARWIN. 



the ganglion are accompanied by capillaries (d), which run 

 either singly, or in pairs, one on each side of the trunk. As 

 they approach the ganglion they give off branches, which 

 anastomose with similar branches of other capillaries, and 

 thus form a network, from which branches pass into the 

 ganglion. In other cases there is no such entwining plexus, 

 and capillaries may be seen simply running up to the 

 ganglion, and entering it in the intervals between the gan- 

 glion cells. 



Having thus briefly described the ganglia and the nerve- 

 trunks, I shall proceed at once to consider their relations to 

 the blood-vessels. Fig. 1 shows, as already stated, that the 

 course of the nerves corresponds in a general way with that 

 of the principal blood-vessels. Fig. 2 is a portion of a 

 nerve-plexus seen with Hartnack No. 4, and shows in a more 

 minute way the character of this relation. A description of 

 this preparation will serve, perhaps, better than remarks of a 

 more general nature, to make the reader acquainted with the 

 usual relations existing between arteries, veins, and nerve- 

 trunks in the bladder of the dog. 



The vessels represented are an artery (a) and a vein (A2), 

 with a large branch given off by each of them. A large 

 nerve-trunk (b), on which are situated a number of ganglia 

 Co), runs parallel with the artery, and at some distance from 

 it ; a somewhat similar trunk runs with the vein. We may 

 call these tAvo, for the sake of convenience in description, the 

 " arterial " and the " venous " nerve-trunks. The venous 

 nerve-trunk is not in reality connected more with the vein 

 than with the artery, and might more fairly be called a 

 second arterial nerve-trunk. Indeed, it does not occur at all 

 in most of my preparations ; what we usually find is an 

 artery accompanied by its vein on one side, and by a gan- 

 glionated nerve-trunk running on its other side. 



The figure shows in Avhat sort of way these two large 

 nerve-trunks, the arterial and the venous, are connected by 

 smaller trunks. The already mentioned branches of the 

 artery and vein are accompanied by a ganglionated nerve- 

 trunk, coming from a large ganglion on the arterial nerve- 

 trunk. 



In addition to the two large nerve-trunks, it Avill be seen 

 that the main artery is accompanied by smaller ones, which 

 are connected with the ganglia of the plexus, especially with 

 those on the arterial nerve-trunk ; these trunks run close to 

 the artery, and are connected with each other by transverse 

 nerves, so as to enclose the artery in a kind of coarse mesh- 

 work. 



