1386 



VEIN. 



ries, in contrast with which the characteristics 

 of the former are most conspicuous. 



The general, the pulmonary, and the portal 

 venous systems may be looked upon as the 

 roots of a tree, the trunks of which would 

 correspond with the auricles and the porta ; 

 or they may be viewed as three cones, the 

 bases of which are the capillaries of each 

 system, and the apices, the auricles, and the 

 porta. In either view, the veins are to be 

 examined, in their track intermediate between 

 these two points, as to their number, size, 

 relation, and modes of dividing and junction. 

 These observations will be carried solely as 

 far as they refer to the general circulation, 

 and that principally as it affects the human 

 subject ; the pulmonary and the portal sys- 

 tems being more properly considered in con- 

 junction with those viscera with which they 

 are connected. 



The venous system is far more extensive 

 than the arterial, both as it regards size and 

 number of vessels. 



Attempts have been made by different ana- 

 tomists to estimate the relative size of arteries 

 and veins, though it is difficult to see upon 

 what data any thing like an exact calculation 

 can be based ; nevertheless, Sauvages states 

 the capacity of veins, as compared with 

 arteries, to be as nine to four, Haller as 

 two to one, and Borelli as four to one. 

 Though it may be impossible to say which 

 of these is the true estimate, it is ob- 

 vious that the disparity between the two sets 

 of vessels is very great. In the extremities 

 and head, indeed everywhere but in the vis- 

 cera, the veins form two distinct sets, the 

 superficial, subcutaneous, veins, and the deep 

 veins accompanying the arteries. These lat- 

 ter, which are called satellite veins (vencs 

 comites), are almost always double two veins 

 accompanying each artery of the same name. 

 " This rule, however, has some exceptions ; in 

 fact there is only one accompanying vein for 

 most of the great arterial trunks, and even for 

 some arteries of moderate size ; lastly, in some 

 few instances there is but one vein to two arte- 

 ries. Thus, there is only one superior and 

 one inferior mesenteric, one renal, and one 

 external iliac, vein, each of which corresponds 

 to the artery of the same name ; but there is 

 only one umbilical vein to two umbilical arte- 

 ries, and there are several suprarenal arteries, 

 but only one suprarenal vein." (CruveithierC) 

 These exceptions, however, are not suffi- 

 ciently numerous to alter the diffuse and 

 branching character of veins. The following 

 apposite quotation upon this head is from 

 Meckel : " It is a universal law with veins, 

 that the branches or ramifications are larger 

 in comparison with the trunks than in the 

 arterial system ; the veins of a part, or even 

 of the whole body, never uniting themselves 

 to so small a number of stems as those out of 

 which the arteries take their origin. The 

 aorta and pulmonary artery originate as single 

 stems out of the respective cavities of the 

 heart; the systemic veins, on the contrary, 

 terminate in three trunks, the superior and 



inferior cavae and the coronary vein ; more- 

 over, the superior cava receives, but just be- 

 fore its entrance into the heart, a fourth 

 trunk the azygos vein. The pulmonary 

 veins terminate in four, five, or even six 

 trunks into the left auricle. Again, in the 

 extremities, take the arm, for instance, 

 where there is but a single artery, there are 

 four considerable venous trunks. Thus divi- 

 sion is the character of the arrangement of the 

 veins ; contratension that of the arrangement 

 of the arteries." (Meckel, Handbuch der 

 menschlichen Anatomie, Band i. S. 201.) 



Origin of Veins. Veins originate, almost 

 without exception, by the capillaries uniting 



increasing in size, and diminishing in num- 

 ber. This fact has been known, and all but 

 universally received, since the days of Mal- 

 pighi, who (in 1661) demonstrated, by micro- 

 scopical research, that portion of Harvey's 

 system of the circulation which had not been 

 displayed, the passage of the blood inter- 

 mediately between the arteries and veins, 

 the capillaries, and thereby explained the 

 origin of the veins. That veins originate only 

 by capillaries has also been generally ad- 

 mitted ; but Haller has described absorbent 

 veins as arising from all free surfaces ; and 

 Cruveilhier speaks of veins commencing with 

 open mouths on the surface of all mucous 

 membranes ; opinions long since refuted. 

 There appear, however, to be some excep- 

 tions to this general rule of capillary origin of 

 veins. Thus, the veins which return the 

 blood from certain portions of erectile tissue 

 would seem to commence as little venous 

 caverns or sacs, into which blood is poured 

 by arteries of a size much above capillary 

 vessels. (Valentin: Mutter.} 



Mr. Paget has recently pointed out another 

 mode of venous origin as occurring in the 

 wing of the bat ( Vesperlilio), where arteries 

 of comparatively considerable size pass at 

 once into veins without intermediate capil- 

 laries. Mr. Paget observes : " Very gene- 

 rally the arteries of the second and third 

 order of branches pass into veins of corre- 

 sponding size without any intermedium of 

 capillaries. The capillaries are rather in the 

 position of offsets from the continuous chan- 

 nels of arterial and venous loops, than in their 

 more ordinary relation as intermediate canals 

 leading from arteries to veins."* Further 

 research, especially in comparative anatomy, 

 will probably exhibit other instances of pecu- 

 liar venous origin. 



Course, Anastomoses, Plexuses, fyc. of Veins. 



In travelling from their commencement to 

 their termination, veins follow very various 

 courses, the most marked differences indi- 

 cating a division into tho^e which accompany 

 their corresponding arteries, and those which 

 pursue an independent course; a division 

 which corresponds, with a few exceptions, to 

 the deep and the superficial veins. 



In commencing, the veins form networks of 



* Lectures on Inflammation, by James Paget, 

 F.R.C.S., in Medical Gazette, vol. xlv. p. 968. 



