BRANCHES OF THE A. SUBCLAVIA. 351 



§ 929. A A. intercostales (10 pairs), (Fig. 103, AA. costales). — The intercostal arteries 

 are given oflF from the dorsal side of the aorta. Each passes to an intercostal space and 

 divides into three branches. One of these passes ventrad along the caudal margin of the 

 cephalic of the two ribs between which it extends (Fig. 103) ; another goes to the deep 

 muscles of the back, and the third enters the spinal canal through the intervertebral 

 foramen ; see i^ 484. 



§ 930. A. bronchialis. — The arteries (2) to the lungs arise either from the aorta itself, 

 about opposite the root of the lung, or from the 4th intercostal arteries. They accompany 

 the bronchi to the lungs. 



§ 931. AA. cesophageaae (2-4), (Fig. 107, A. oes.). — These are all small branches and 

 may sometimes arise from the intercostals instead of the aorta. 



§ 932. AA. lumbales (2-3 pairs). — On account of the great caudal projection of the 

 diaphragm, 2-3 pairs of the lumbar arteries are given off by the thoracic aorta. Rarely 

 also the ..4. cceliaca arises in the thorax (§ 966). 



§ 933. A. subclavia dextra (Fig. 102, A. sbclv. dext.\— This is 

 a continnation of the A. hracTiio-cephalica peripherad of the origin 

 of the right carotid. Tear away carefully any connective tissue cov- 

 ering it as far peripherad as the ectal margin of the first rib. Note 

 the large nerve covering its ventral face. This is the vagus (Fig. 

 107 and 108 ; the recurrent laryngeal branch may be seen winding 

 around to its dorsal side (Fig. 108, N. 1. r.). 



Branches op the A. Subclavia. 



§ 934. A. vertebralis. — This, the first branch, arises from the 

 cephalic surface of the subclavian and passes dorso-cephalad to 

 enter the vertebrarterial canal. It passes through this to the brain 

 (Fig. 102, 103, A. vert., 104, A. vrt.). In Fig. 104, the dorsal waU 

 of the vertebrarterial canal is removed and the artery shows 

 throughout nearly its whole extent. 



§ 935. A. sternalis s. mammaria interna (Fig. 101, A. strn., 

 102, A. strn., 103, 107). — This arises from the ventral surface of the 

 A. suhclama nearly opposite the origin of the A. vertebralis. It 

 passes ventrad and reaches the sternum opposite the 2d mesoster- 

 neber (Fig. 49). It sends two or three small branches cephalad, 

 then extends caudad along the sternum, and, as stated above, is 

 laterad of the sternal vein. Branches of this artery anastomose 

 with the intercostal arteries (§ 929), with the phrenic on the dia- 

 phragm, and with the epigastric on the abdomen (Fig. 101). The 

 left sternal also usually supplies the A. pericardiaca to the peri- 

 cardium. 



§ 936. A. intercostalis superior (Fig. 102, A. cstl. superior). — 

 Just as the subclavian crosses the first rib, this artery arises from 



