­Syn.: Thoracique interne; mammaria interna; -Innere Brustpulsader.

The internal mammary artery, of a lower diameter than the one of the vertebral artery, is remarkable by the extent of its course and by the multiplicity of its branches; it arises from the former face of the subclavian artery, at 3 or 4 mm apart from the vertebral artery. From its origin, it goes bottom, ahead, and a little medialward and reaches the posterior face of the first costal cartilage; there, it becomes vertical, perpendicularly crosses the posterior face of the first six costal cartilages, and, at the level of the sternal end of the sixth intercostal space, is divided into two terminal sections, one intern and the other extern.

 

Relations of the internal mammary artery

At the level of the neck, the internal mammary artery, which answers at the internal end of the clavicle, runs between the pleural dome on the former slope of which it is applied and the lower face of the subclavian vein. At this level, it is crossed by the phrenic nerve which, initially located frontward and apart from the artery, passes behind and in it, circumventing its inner face. In the thorax, the internal mammary artery is in connection behind with the parietal layer of the pleura, of which it is separate ahead starting from the third rib by the triangular muscle of the sternum it answers the posterior face of the first six costal cartilages and the internal intercostal muscles. It skirts the edge of the sternum at a distance from 5 to 15mm, this distance is very variable. On the level of the first space, the distance oscillates between 6 and 20 mm; on the level of the second, it varies between 10 and 20 mm; on the level of the third, between 10 and 21 mm on the level of the fourth, between 8 and 25 mm on the level of the fifth, between 7 and 35 mm on the level of the sixth finally, between 6 and 45 millimeters.

The mammary is accompanied by two veins and a chain of lymphatic ganglia. The two veins are not always in contact with the artery; on some subjects, the unit formed by the three vessels can reach a width of 1 cm.

Collateral branches of the internal mammary artery

In its way, the internal mammary artery provides many collateral branches. One can divide them into posterior, external and former.

The posterior branches are arteries which are distributed to the thymus or with the grease which replaces it; pericardial arteries, which go on the former face of the pericardium, and a more important artery, the higher diaphragmatic artery. This artery goes behind and in bottom and will join the phrenic nerve, on with dimensions intern of which she places herself. From rather reduced gauge, it goes down with the nerve between the pleura and the pericardium to the higher face from the diaphragm, in which it finishes while being anastomosed with diaphragmatic the lower. In its way, it very provides some branches hails to the mediastinal pleura, the thymus, the phrenic nerve and the pericardium.

The internal branches are the intercostals arteries former two for each space, one higher, other the lower, these arteries move obliquely in bottom and outwards, because they are born a little above the space to which they go. Initially located between the triangular one and the intercostal intern, they perforate this last muscle and are placed in front of him. They finish have anastomosing itself with full channel with the final part of the aortic intercostales. The volume of these arteries is more variable it is not rare to see one or more of them being lacking.

The former branches still called perforating branches, are of number equal to that of intercostal spaces which the internal mammary artery crosses.

They perforate the internal part of the intercostal space and are distributed to the pectoral large muscle, the mammary gland and the skin. On the woman, especially on pregnant woman, the branches which go to the mammary gland become very flexuous and take a great volume; Cruveilhier saw them reaching the gauge of radial.

Terminal sections of the internal mammary artery

The terminal sections are two, one external or thoracic the other intern or musculo-phrenic.
The external or thoracic branch moves in bottom and outwards, forming with the trunk of the internal mammary artery an obtuse angle open in top and outwards.

It walks on the level of insertions of the diaphragm, behind of the cartilaginous edge of the borrom opening of the thorax. To the level C each intercostal space, it gives one or two branches which offer the same provision as the intercostals branches come from the trunk of the internal mammary artery. It provides many branches to the diaphragm and finishes, in general, at the level of the tenth space, seldom of eleventh.

The internal or abdominal branch, usually less bulky than the external one, continues the direction of the principal trunk, leaves the thoracic cavity while passing in the cellulous interstice which separates the sternal beams from the costal beams of the diaphragm and penetrates in the sheath of the right muscle.

Before penetrating in this sheath, it emits a small branch which moves transversely in inside, either ahead, or behind of the appendix xiphoïde and anastomosis on the level of the line of centers with a similar branch on the opposite side. Arrived in the sheath of the musculus rectus abdominis, it walks on initially between this aponevrotic envelope and the fleshy body of the muscle and finishes while being anastomosed with the epigastric one, towards the umbilical area.

The  internal mammary arteries, their abdominal branches and the épigastric ones constitute, in the anterior wall of the thorax and the abdomen, a double vertical anastomosis between the higher aortic system and the inferior. Moreover, the thoracic intercostals and the lumbar ones, being linked with the intercostals mammaries, form as many hyphens between great anastomosis and the aortic system.

Varieties of the internal mammary artery

It is extremely rare that the internal mammary artery is completely lacking, but one can see it considerably reduced volume. It is sometimes double of each dimension. The varieties of origin are multiple; it is frequently born from the subclavian with one of the other branches of this artery; one saw it still being born from the aorta, the brachio-cephalic trunk and even from the axillary. One saw it leaving the thorax by an intercostal space and returning there by subjacent space. Mammaire interns additional

One parallel to gives this name to an artery which goes down under the plèvre, the mammaire intern. Announced for the first time by Otto which called it “ramus costalis lateralis sive intercostalis”, it was observed by Tiedeman, Hodges, Henle which call it mammaire side intern, Hyrtl which gives it the name of medial intercostal artery . More recently, Rieffel have observed a case: the artery, born from the subclavian, extended to the fourth intercostal space , it gave an anterior and a posterior branche for each space.

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