ANATOMY. 



3. Arteries in general do not pursue a 

 straight, but a serpentine course ; this is 

 remarkably the case in some instances; 

 as in the spermatics, those of the face and 

 occiput, and in most of the smaller arte- 

 ries. 



4. Though the ramification of arteries 

 may be compared to the branching of 

 trees, yet it differs materially in this par- 

 ticular, that the different branches fre- 

 quently conjoin. This conjunction is tech- 

 nically*termed,if we borrow the term from 

 the Greek language, their anastomosis ; if 

 from the Latin, their inosculation. This 

 union of arteries rarely happens among 

 the larger ones, but frequently among the 

 smaller ; and increases in number in pro- 

 portion to the minuteness of the vessels. 

 The utility of the inosculations of arteries 

 is evident; were it not for this circum- 

 stsnce, if any arterial trunk were acci- 

 dentally compressed, so that the current 

 of blood in it should be for some time 

 obstructed, the parts which it supplied 

 must perish. But in consequence of the 

 frequent communications of these tubes 

 with each other, the blood can pass from 

 the adjacent arteries into all the branch- 

 es of any one accidentally obstructed. 



When arteries inosculate, two currents 

 o^ blood, moving in opposite directions, 

 must come together, and retard each 

 other's motion. This probably is the rea- 

 son, why larger arteries, in which the 

 blood flows with rapidity, so seldom con- 

 join ; whilst the smaller ones in which the 

 blood's motion is more tardy, communi- 

 cate in surprising numbers, and with a 

 frequency proportionate to their minute- 

 ness. The very frequent communications 

 of the minute arteries prevent the preju- 

 dicial consequences of obstruction of the 

 trunks almost as effectually, as if those 

 arteries themselves communicated by 

 more direct and larger channels. 



All these minute arterial tubes are capa- 

 ble of enlargement ; and it is an ascertain- 

 ed fact, that even the aorta itself may be 

 gradually obstructed at some distance 

 from the heart, without the parts which it 

 supplies being deprived of nourishment. 

 From an attentive consideration of all 

 these circumstances it has been conclud- 

 ed, that the moderate increase of the 

 area of the branches of large arteries ; the 

 ucute angles at which they divide ; their 

 nearly rectilinear course ; and the rare oc- 

 currence of inosculation between them ; 

 are designed to facilitate the rapid motion 

 of the blood in them, so that it may arrive 

 unchanged, and in the same state that it 

 was in when projected from the heai't, at 

 that part of the body, for the nourishment 



of which it was intended : whilst, on the 

 contrary, the great increase of the area of 

 the smaller vessels, the variety of their 

 angles, their tortuous course, and their 

 frequent communications, were designed 

 to check the velocity of the blood's mo- 

 tion, when it has arrived at that part where 

 secretion is to be performed, and nutri- 

 tion is to take place. Contrary opinions 

 have indeed been maintained ; and for the 

 further discussion of this subject, we must 

 refer the reader to the remarks on the 

 circulation in the article PHYSIOLOGY. 



Termination of the arteries. When these 

 vessels have become very minute, they 

 terminate in two ways : they either turn 

 back again, and become veins, and return 

 the blood to the heart, or they send off" 

 fine vessels, which abstract something 

 from the circulating blood, and are there- 

 fore called secerning arteries. Though 

 none but minute arteries are ever reflect- 

 ed to become veins, yet many of them are 

 of sufficient magnitude to admit common 

 waxen injection ; and when this experi- 

 ment succeeds, the continuity of the ar- 

 teries and veins is very manifest. It seems 

 therefore to follow from this facility of 

 communication, that the mass of the blood 

 is constanntly and freely circulating, in 

 order to undergo that change which is ef- 

 fected in the lungs, whilst but a small part 

 of it proceeds into the verv" minute arte- 

 ries, for the purpose of having secretions 

 made from it. For these arteries, however 

 minute, mustbe considered large, in com- 

 parison with the exility of others, which 

 cannot be injected with wax, and even 

 reject the red globules of the blood, or 

 admit them in such small proportion, that 

 they do not impart the red colour to the 

 fluid which moves in those vessels. Now, 

 we may venture to affirm that these glo- 

 bules do not much exceed in diameter 

 the 150,000th part of an inch, which cir- 

 cumstance sufficiently sho\vs the minute- 

 ness of the lesser arteries. 



The secerning arteries are in general 

 too minute to admit of demonstration ; 

 they are however evident in some glands ; 

 in the kidney, for instance, they may be 

 seen continued into the excretory vessels. 

 Subtile injections, when thrown into the 

 larger arterial trunks, ooze out on the sur- 

 faces of membranes, and into the cellular 

 substance, and they are generally suppos- 

 ed to be poured forth from the open orifi. 

 ces of secerning arteries. Analogy, there- 

 fore, rather than actual demonstration, 

 leads us to believe, that the secerning arte- 

 ries abstract the particles of nutrition, or 

 the materials which compose the fabric of 

 the body, from the circulating fluids, and 



