204 PRACTICAL ANATOMY. 



The internal mammary artery has the following branches, all of which you 

 can easily find : 



1. The perforating branches that come through the five or six upper inter- 

 costal spaces and supply the major pectoral muscle and the mammary gland. 



2. The mediastinal branches to the mediastinal connective tissue and glands 

 under the sternum. They also supply the thymus gland in the foetus or its 

 remains in the adult, hence they are called also tliyinic 'arteries. 



3. The sternal branches, quite small and numerous, to the sternum and tri- 

 angularis sterni muscle. 



4. Pericardiac brandies to the anterior surface of the pericardium. 



5. The comes nervi phrenici is a long, slender artery that accompanies the 

 phrenic nerve to the diaphragm. You will find this nerve between the pleura 

 and pericardium. 



6. The anterior intercostals supply the six upper intercostal spaces. There 

 are two in each space, one above and one below. They anastomose with the 

 posterior intercostal arteries from the aorta. 



7. The musculo-phrenic, that furnishes the anterior intercostal arteries to the 

 remaining spaces. It also supplies branches to the diaphragm. 



8. The superior epigastric passes through the diaphragm between its costal 

 and sternal parts, enters the sheath of the rectus muscle, finally the muscle itself, 

 and anastomoses with the deep epigastric branch of the external iliac artery. 



The internal mammary artery is a branch of the subclavian, as you saw when 

 you dissected the neck. Its parietal branches are to the anterior walls of the 

 thorax what the parietal branches of the aorta are to the posterior walls of the 

 thorax. Now go down between the sixth and seventh cartilages and find where 

 the artery divides into the musculo-phrenic and superior epigastric. 



The thoracic walls are supplied with blood, then, by intercostal arteries. 

 These arteries come : (i) From the aorta ;' (2) from the internal mammary ; (3) 

 from the subclavian ; this latter furnishing the artery to the superior intercostal 

 space. The blood from this area is collected and delivered as follows : the first 

 or superior intercostal vein is tributary to the vertebral vein ; the others to the 

 azygos veins, in the posterior mediastinal space, to be presently dissected. 



The triangularis sterni muscle arises from the lateral aspect of th( 

 sternum, and is inserted into the cartilages of the third, fourth, fifth, and sixtl 

 ribs. 



INTERIOR OF THE THORAX. 



Geometrically the thorax possesses : 



1. An apex, through which pass : (i) The oesophagus ; (2) the trachea ; 

 common carotid artery on the left, and the innominate artery on the right side ; 

 (4) the phrenic, pneumogastric, sympathetic, and recurrent laryngeal nerves ; (5) 

 the internal jugular and subclavian veins ; (6) the thoracic duct ; (7) the sterno- 

 hyoid and sterno-thyroid muscles ; (8) the third and fourth layers of deep cervi 

 cal fascia form the pericardium and invest the longus colli muscle respectively ; 

 (9) the subclavian artery on the left side. 



2. A base, formed by the diaphragm. This is a niusculo-aponeurotic struc- 

 ture, in relation with the pleurae and pericardium above and below with the 

 peritoneum. It transmits: (i) The aorta; (2) the ascending vena cava ; (3) tin- 

 (i-sophagus and pneumogastric nerves; (4) the superior epigastric branch of the 

 internal mammary artery ; (5) the thoracic duct ; (6) the communicating branch 

 from the lumbar veins to the a/ygos veins. 





