1378 



VEIN. 



in the middle of the vein, and are there 

 united by the contact of their margins ; and 

 so accurate is the adaptation, that neither by 

 the eye, nor by any other means, can the 

 slightest chink along the line of contact be 

 perceived. But if the probe be now intro- 

 duced from the extreme towards the more 

 central parts, the valves, like the flood-gates 

 of a river, give way, and are most readily 

 pushed aside."* 



Valves exist in two different situations ; 

 namely, at the orifices of lesser veins where 

 they join the trunks which they supply, and 

 in the canals of veins, arranged at various 

 points. 



Fig. 863. 



Diagram exhibiting different forms of Valves. 



a, valve placed at the orifice of the renal vein in the 

 sheep, seen in face ; a', the same in ideal section ; 

 b, the ordinary semilunar valve from the tube of a 

 vein ; V, the same in section ; c, imperfect valve at 

 orifice of intercostal vein ; </, section of imperfect 

 valve at orifice of hepatic vein ; d, the same in 

 face (the dotted lines in a, c and d correspond to the 

 orifices of the respective veins) ; e, very imperfect 

 valve ; e', the same in section ; /, plan of double 

 valve at orifice of vein ; ft, the same in section ; 

 g, ideal section of small valve and sinus ; h, sec- 

 tion of sinus without a valve. 



At the orifices of veins the valves are either 

 single or double: when single, the free margin 

 always looks towards the heart. In the canals 

 of veins the valves are usually double in the 

 larger, and single in the smaller. It is rare, 

 in the human subject, to find them in threes 



* Loc. cit. 



on the same plane, though it has been found 

 both by Morgagni and Haller ; but in the great 

 vessels of the larger mammalia it is common. 

 There are none in the capillaries ; but, accord- 

 ing to Henle, in veins of not more than half 

 a line in diameter, they make their appear- 

 ance. 



For the purposes of anatomical description 

 a valve may be said to have a body, margins, 

 and cornua. The body of the valve has a 

 cardiac, concave, or proximal face and a convex 

 or distal face. The margins are, the free, 

 or that which is unattached, and the attached 

 margin. The cornua are the angles formed by 

 the meeting of the two margins, and constitute 

 the extreme lateral boundaries of the valve. 



Valves differ from each other very con- 

 siderably in form, varying from a mere linear 

 elevation on the inner surface, in which the 

 probe scarcely hitches as it is pushed along, 

 to others which almost form a long isosceles 

 triangle. The outline of the margins deter- 

 mines the form of a valve. Cruveilhier says 

 that the free margin is always straight ; but 

 this is not the fact, though it is always more 

 so than the attached. 



In the first attempt at a valvular formation 

 there is merely a slight elevation of the inner 

 surface, and the free and attached margins 

 are nearly parallel : these scarcely constitute 

 valves. (Fig. 863. e,^.) 



Valves, still imperfect but of larger dimen- 

 sions, are found at the orifices of veins, as well 

 as in their canals. When existing in the former 

 situation (and this is applicable to all valves 

 thus placed), their attached margin corres- 

 ponds with the side of the orifice which is 

 furthest from the heart, and the outline of 

 this margin is determined by the form of the 

 vessel's mouth. If the lesser vessel joins the 

 greater at right angles, the opening will be 

 circular, and the attached margin of the valve 

 a semicircle. If, however, the junction be ob- 

 lique, and an acute angle be formed by the 

 two vessels, then the margin attached will be 

 drawn out of the semicircle, so as to form a 

 sort of apex in the centre. The former of 

 these conditions is shown at fig. 863. c, taken 

 from a small valve at the orifice of an inter- 

 costal vein, joining the azygos ; and the latter 

 is represented at d, which is a drawing made 

 from a valve at the orifice of an hepatic vein, 

 where it joins the vena cava : c' is an ideal 

 section of the same. The dotted line in a,c and 

 d represents, in conjunction with the line 

 of the attached margin of the valve, the orifice 

 of the tributary vein. 



The next form, in order, and the one which 

 is the most common, is the semi-lunar* valve, 

 as it is ordinarily found in the tube of valved 

 veins, the attached margin being nearly semi- 

 circular, and the free nearly straight (fig. 

 863. b). It was probably of these valves that 

 Haller spoke when he said that the attached 

 margin of valves constitutes a parabolic curve : 

 it may be applicable to some of the semi-lunar, 



* Fabricius, not inaptly, described them as re- 

 sembling a finger nail, " forma ostiolorum ea est, 

 ut indicis unguem imitentur." Loc. cit. p. 151. 



