1382 



VEIN. 



senting a vein from the oesophagus of an eel, 

 magnified with low power, the vasa vasorum 

 are seen to supply, indiscriminately, the vessel's 

 coats and some small pellets of adipose tissue 

 which were near it. The arteries, nourishing 

 a vein, ramify and divide principally upon, and 

 among, its cellular coat, and form an elaborate 

 plexus, with meshes having a general longi- 

 tudinal direction, as seen in the figure ; which, 



Fig. 866. 



I 



' Vasa Vasorum on external surface of a small Vein 

 from the oesophagus of eel. (Anyuilla acutirostris.) 



a a, vein ; b b b, small arteries supplying indiscrimi- 

 nately the venous tunics and small masses of fat 

 around the vein ; c c c c c, granules of adipose 

 tissue. Natural injection. (Magnified about 18 

 diameters.) 



though drawn from a fish, sufficiently indicates 

 the condition as found in man and mammals. 

 The arrangement of these capillaries is, how- 

 ever, subject to variety : in the vena cava of 

 the cod, I have seen them long, straight, even, 

 and perfectly parallel, with scarcely any trans- 

 verse branching or anastomosis. The little 

 venous trunks of the vasa vasorum usually 

 open directly into the cavity of the vein, 

 among whose tunics they have previously 

 ramified, and their course is quite independent 

 of the corresponding arteries. (Hen/e.) 



The vasa vasorum principally exist in the 

 areolar tunic, but Henle states that they are 

 to be found abundantly among the annular 

 fibres of the veins.* The internal longitu- 

 dinal coat is, in all cases, extra-vascular. 



Nerves of veins. As far as our knowledge 

 hitherto goes, veins differ remarkably from 

 arteries in rantly being made the support of 



* In arteries, Weber has never found them in the 

 circular tunic. Burdaeh states that he has found 

 a few. 



nerves, and in seldom receiving any distribu- 

 tion of them to their coats. It is a remark- 

 able circumstance that veins appear, with 

 slight exceptions, to be separated from nerves. 

 The exceptions to this rule are few and in- 

 considerable. 



The inferior vena cava receives some small 

 filaments from the diaphragmatic ganglion of 

 the sympathetic, just below the diaphragm. 

 The vena porta supports and is entwined by 

 the branches of the hepatic plexus, which it 

 conducts to the liver. Pappenheim describes 

 some nerves as being distributed to the cere- 

 bral veins. Bidder states that he has traced 

 some filaments of the fourth cerebral nerve 

 to the lateral sinus : and Wrisberg describes 

 a nervous plexus as surrounding the facial 

 vein, which he ingeniously imagines may cause 

 contractions of the vein, and thereby pro- 

 duce that congestion of the face constituting 

 blushing. 



In the cod-fish (Gadus morrhua), I have 

 traced nerves from the auricle down upon the 

 venous sinus immediately below it : these 

 formed loops in the walls of the sinus, and 

 appeared to return to the heart. The nerves 

 in question are doubtless a continuation of 

 the cardiac nerves ; and, in all probability, 

 bear the same relation to the rhythmical action 

 of this pulsating cavity, which the other car- 

 diac nerves do to the cavities of the heart 

 itself. 



It is very probable that some such nervous 

 supply is furnished to those parts of the veins 

 of nia'n and mammals, near the heart, in which 

 cardiac muscle is found. 



It may, perhaps, be still a question whether 

 the almost complete non-nervous character 

 of veins is absolutely correct, and whether the 

 paucity or tenuity of the nerves, supplied to 

 .veins in general, be not the reason why they 

 have as yet eluded observation ; for analogy 

 scarcely justifies the idea of organs possessing 

 muscular tissue and still being destitute of 

 nerves. This opinion is strengthened by the 

 fact that arteries, having the same sort of 

 muscularity as veins, though in larger amount, 

 are regularly supplied with nerves. 



Comparative structure. I am not aware 

 of any observations upon the comparative 

 structure of veins in birds and reptiles. Those 

 that I have myself made are principally in- 

 troduced under the heads, Fenestrated mem- 

 brane, Epithelium, fyc. 



In Birds, the venous walls are composed 

 principally of areolar tissue, external to the 

 lining membrane; and I have observed that 

 in the diving-birds, the vena cava posterior is 

 composed almost solely of elastic tissue. 

 There are no muscle-cells in the cerebral 

 veins of birds. 



In Fishes, the venous parietes appear to be 

 formed of a sort of areolar tissue longitudi- 

 nally disposed. Embedded in the walls of 

 the veins there is an abundance of pigment, 

 which exists in greater quantity in the inter- 

 costal veins, and those tributary to the car- 

 dinal vein. This pigment is of the variety 

 called by Schwann " stellate pigment cells," 



