THE THORAX. 211 



The Thymus Gland or Body. You will find the fibrous remains of this 

 gland on the anterior part of the pericardium in the adult, in the anterior inedias- 

 tinal space. This gland is a structure of foetal life ; in children two years old it is 

 quite large. (Fig. 147.) In the four months' foetus the thymus is in appearance 

 like the lung, on casual examination, and is frequently mistaken for this organ 

 by the novice. 



The cardiac root structures are : 



1. The coronary, or nutrient, artery to the heart, from the aorta. 



2. The voice cavo?, coming from the whole body with venous blood. 



3. The pulmonary arteries, conveying blood to the lungs. 



4. The pulmonary veins, returning blood from the lungs. 



5. The aorta, distributing blood to the whole body. 



6. The cardiac branches, from the sympathetic and vagus nerve. 



How to Study Relations of These Structures Which You liavc UOT.V Exposed, 



SUPERIOR LOBE OF RIGHT LUNG 



Aorta 



Pulmonary artery 

 flIGHT AURICULAS APPENDIX 

 MIDDLE LOBE 



OUCTUS ARTERIOSUS 



Pulmonary artery 



SUPERIOR LOBE OF LEFT 

 LUNG 



. LEFT AURICULAR APPENDIX 



~i j Pulmonary artery 



INFERIOR LOBE 

 i Descending aorta 



FIG. 149. ANTERIOR VIEW OF FCETAL HEART, VESSELS, AND LUNGS. 



Regardless of the Particular Arbitrary Space (Fig. 145). (i) Locate in the mid- 

 dle the ascending part of the arch of the aorta (Fig. 153); (2) to the right of this 

 is the descending vena cava above and the ascending vena cava below ; (3) to 

 the left of the aorta is the common pulmonary artery. The remaining struc- 

 tures are the pulmonary veins, which may be seen by turning the apex of the 

 heart toward the right sjioulder. 



Notice now particularly the pulmonary artery (Fig. 148), for it is the one 

 structure in this root that complicates relations. At its origin it overlaps the 

 first part of the aorta ; separate these vessels the aorta from the pulmonary 

 artery. Next it divides into a right pulmonary and a left pulmonary. The left 

 pulmotiary passes to the left lung, in front of the descending aorta and left 

 bronchus. The right pulmonary artery passes to the right lung, behind (i) the 

 aorta, (2) the vena cava, (3) the phrenic nerve and its artery, and (4) below the 

 right bronchus. 



The ductus arteriosus (Fig. 149) in the foetus is a vessel connecting the pul- 



