516 THE ARTERIES. 



made amply conspicuous in the following description, is their bifurcation or 

 dichotomous arrangement, which prevails so largely.) 



COURSE. In the course pursued by an artery, it is necessary to consider 

 the situation occupied by the vessel, its direction, relations, and the anastomoses 

 which establish communication between it and the neighbouring vessels. 



Situation. The arteries tend constantly to recede from the superficial 

 parts : to become lodged in the deep-seated regions, and in this way to be 

 removed from the hurtful action of external causes, a tendency all the more 

 marked as the arteries are more considerable in volume, and which ceases to 

 be manifested in the less important ramuscules. These vessels, therefore, 

 occupy either the great cavities of the trunk, or the deep interstices on the 

 internal face of the members ; when they pass over an articulation, it is 

 always on the side at which flexion occurs. But in the limbs, for instance, 

 the joints are flexed alternately in opposite directions, and it then happens 

 that the arteries in these regions have a slightly helicoid (or spiral) disposi- 

 tion. This is evident in the case of the femoral artery, which passes round 

 the inner face of the femur to become the popliteal artery ; and also in the 

 humeral artery, which is at first situated to the inner side of the scapulo- 

 humeral articulation, then turns around the humerus to be placed in front of 

 the elbow joint. 



Direction. The arteries are sometimes rectilinear, and at other times 

 more or less flexous. The latter disposition is evidently intended to prevent 

 the dilaceration of the vessels in organs susceptible of elongation and con- 

 traction, as may be remarked in the tongue or to moderate the impetus of 

 the blood, as in the internal carotid arteries. 



Eelations. In their course, the arteries may be in contact with the 

 viscera, nerves, muscles, bones, skin, and connective tissue. 



a. In nearly every part of the body, the arteries maintain the most 

 intimate relations with the veins : sometimes with two of these vessels, when 

 the artery is placed between them ; sometimes with only one, which is always 

 more superficial. 



b. The arteries are usually accompanied by nerves belonging to the 

 cerebro-spinal or ganglionic systems. Those of the latter category are 

 distinguished by the reticular interlacing they form around the visceral 

 arteries ; their structure will be alluded to presently. 



c. Lodged for the most part in the interstices of the muscles, the arteries 

 contract relations with these organs which it is very important to know in a 

 surgical point of view. Some of these muscles lie parallel with important 

 arteries, and for this reason have been designated satellite muscUs ; they 

 serve to guide the surgeon in searching for the arteries, by the more or less 

 salient relief their presence affords beneath the skin. 



It is worthy of remark that the arteries are not included in the fibrous 

 sheaths enveloping the muscles ; these vessels nearly always occupy, with 

 the nerves which accompany them, special lodgments resulting from the 

 approximation of several aponeurotic sheaths. When they pass through 

 the substance of a muscle, which sometimes happens, they are covered 

 by an arch or fibrous ring, which protects them from compression during 

 muscular contraction : the arch or ring receiving on its convexity the 

 insertion of fibres from the muscle. 



d. Nothing is more common than to see the arteries in direct contact 

 with the bones : as, for instance, the aorta, intercostals, &c. Neither is it 

 very rare to find a more or less thick muscular layer between the arteries 

 and portions of the skeleton. In every case, a knowledge of the connections 



