764 HUMAN ANATOMY. 



the external iliac, and thus connects the superior and inferior portions of the aortic 

 system of vessels. In addition, by means of the anterior intercostals, it makes 

 extensive connections with the thoracic aorta through the. aortic intercostals. 



Variations. — The internal mammary may arise from the second or even the third portion 

 of the subclavian, or it may take its origin from the thyroid axis or from the superior intercostal. 

 In its course down the anterior thoracic wall it varies considerably in its relation to the lateral 

 border of the sternum, its distance from it varying in different cases from 5-20 mm. 



Of the supernumerary branches to which it may give rise, one of the most important is the 

 lateral internal mammary (ramus costalis lateralis). This arises from the internal mammary 

 above the first rib, or in some cases directly from the subclavian, and descends upon the inner 

 surfaces of the upper four or six ribs and the intervening intercostal spaces, parallel with the 

 internal mammary, but some distance lateral to it. It gives off branches in each intercostal 

 space, which anastomose ventrally with the anterior intercostal branches of the internal 

 mammary and dorsally with the aortic intercostals. 



Practical Considerations. — The internal mammary is not infrequently 

 involved in stab wounds of the chest, and this accident may be suspected if after such 

 a wound there are threatening symptoms of internal hemorrhage with no evidence of 

 injury to the lung itself. The bleeding may take place into the pleural cavity, causing 

 the characteristic symptoms of haemothorax (page 1866). 



Compression. — In emergencies the bleeding may sometimes be arrested by 

 pushing through the wound into the intrathoracic space or pleural cavity a pouch of 

 antiseptic gauze, packing it with other strips of gauze so as to distend the portion 

 within the ribs, and then making traction upon it so as to compress the wounded 

 vessel against the costal cartilages and the chest-wall. 



This same method is applicable in some cases of hitercostal hemorrhage when it 

 is not possible or desirable to approach the vessel directly in its groove on the under 

 and in'ner border of the rib by incision or by resection of a portion of the rib. 



Ligation. — In some cases it may be necessary to ligate the vessel in its con- 

 tinuity, although its free anastomoses make it very desirable to find and tie it on both 

 sides of the wound. It may be reached through an incision parallel with the sternum 

 and a half-inch from its margin or through a transverse incision extending outward 

 along an intercostal space. In either event, the skin, superficial fascia, sternal fibres 

 of the great pectoral muscle, the external intercostal aponeurosis (connecting the 

 external intercostal muscle with the sternum), and the internal intercostal muscle 

 must be divided. The artery with its accompanying veins will be found in loose 

 cellular tissue lying, in the first two spaces, upon the endothoracic fascia, which sepa- 

 rates it from the pleura ; in the lower spaces the vessel rests upon the triangularis 

 sterni muscle. Below the third or fourth space resection of a cartilage will usually 

 be necessary for the purpose of gaining room, and at any level is often resorted to 

 to permit direct access to the bleeding ends. 



3. The Superior Intercostal Artery. — The superior intercostal artery 

 (truncus costocervicalis) (Fig. 695) arises from the upper posterior surface of the 

 subclavian artery, usually about opposite the origin of the internal mammary, but quite 

 frequently; and especially upon the right side, under cover of the scalenus anticus. 

 It passes at first upward and medially, and then curves backward and downward over 

 the dome of the pleura to reach the anterior surface of the neck of the first rib, 

 where it divides into two terminal branches which pass laterally in the first and 

 second intercostal spaces. As it enters the thorax, the superior intercostal lies be- 

 tween the first thoracic sympathetic ganglion and the first thoracic spinal nerve. 



Branches. — The superior intercostal gives rise to (i) Ihe deep cervical artery, and to 

 two terminal branches, (2) they?;'.?/ and (3) the second intercostal arteries. 



(a) The deep cervical artery (a. cervicalis profunda) arises just as the superior intercostal 

 reaches the upper border of the neck of the first rib, although occasionally it takes origin 

 directly from the subclavian. It is directed upward and backward, passing between the last 

 cervical and first thoracic nerves and beneath the transverse process of the last cervical verte- 

 bra, and ascends the neck between the complexus and the semispinalis colli, to which it sends 

 braTiches. It anastomoses with branches of the ascending cervical, vertebral, and princeps cer- 

 vicis arteries, and gives off a spinal branch which passes along the eighth cervical nerve to the 



