602 THE ARTERIES. 



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, from 

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

 arteries, and for this reason have been designated satellite muscles ; 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 wiiich accompany them, special lodgments from the approximation of 

 several aponeurotic sheatlis. When they pass through the substance of a muscle 

 — which sometimes happens — they are covered by a fibrous arch or 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 relation with 

 the bones — as, for instance, the aorta, intercostals, etc. Neither is it very rare 

 to find a more or less thick layer of muscle between the arteries and portions of 

 the skeleton. In every case, a knowledge of the relations between the arteries and 

 bones is important to the surgeon ; as it enables him to interrupt the circu- 

 lation temporarily in these vessels, by exercising external pressure on the points 

 of their course which correspond to the several bones, and thus diminish their 

 calibre by flattening them. 



e. In consequence of their deep situation, the arteries are, in general, distant 

 from the skin ; there are, nevertheless, some which course immediately beneath| 

 that membrane ; but these are only found about the head and in the extremities. 



/. Lastly, all the arteries are enveloped by a layer of connective tissue, which 

 forms around them a kind of sheath, generally difficult to tear with the fingers, 

 and which isolates from the neighbouring parts, but chiefly the veins. This 

 connective tissue — more or less abundant according to the regions — is always loose 

 enough to allow the arteries to roll and be displaced with the greatest facility, 

 and thus to glide away from sharp bodies accidentally introduced into the tissues. 



Anastomoses. — Very often the arteries are united to each other by communi- 

 cations, which have received the name of anastomoses, and which assure the 

 equable distribution of the blood in regulating its flow. There are distinguished : 



1. Anastomoses hy convergence — formed by two vessels joining at their 

 terminal extremity in an angular manner, to form a third and more voluminous 

 trunk. 



2. Anastomoses hy arches or hy inosculation — due to the junction of two 

 principal branches, which are inflected towards each other, meet, and unite to 

 form a single and curvilinear canal. 



3. Anastomoses hy transverse communication — represented by ramifications 

 thrown transversely between two parallel arteries. 



4. Mixed or composite anastomoses — in which are found a combination of the 

 different types enumerated above. 



A knowledge of the anastomoses of vessels is of the highest practical interest ; 

 as these communications permit the surgeon, in extreme cases, to tie the principal 

 artery of a region without the latter experiencing any considerable nutritive 

 disturbance ; the blood continuing to amve by the collateral vessels which, at 

 first very small, gradually dilate from the eccentric pressure to which their walls 



