TOPOGRAPHY OF THE THORAX AND ABDOMEN 27 



left one is separated from the trachea by the aortic arch, 

 while the right one lies between the trachea and the lung 

 (Plates VI and VII). The right recurrent laryngeal nerve 

 does not come into close relation with the trachea. The 

 left recurrent lies in the left angle between the oesopha- 

 gus and the trachea from the under part of the arch of the 

 aorta to the larynx. 



Mehnert' places the bifurcation of the trachea opposite 

 the fifth or sixth thoracic vertebra and in old age as low 

 as the seventh vertebra. 



THE HEART 



The heart is seen in section in Plates VIII to XII and 

 in projection in Plates XXVIII, XXX, XXXI, XXXII, 

 XXXIV and XXXV. The base lies between the second 

 sternochondral articulations and the lower half of the 

 fifth thoracic vertebra. The apex though poorly defined, 

 may be located behind the fifth left costochondral articu- 

 lation, about 7 cm. from the midline, at the level of the 

 xiphosternal articulation and the lower border of the ninth 

 thoracic vertebra. The surface form of the heart may be 

 seen in Plate XXVIII. The base is represented by a line 

 through the middle of the second sternochondral articula- 

 tions. The right border lies entirely to the right of the 

 sternum and extends from the lower part of the second right 

 costal cartilage near the sternum, to the upper border of the 

 fifth cartilage about 3 cm. from the midline. Its greatest dis- 

 tance to the right of the midline is at the lower end. The 

 inferior border extends nearly in a straight line from the 

 lower end of the right border to the apex point. It crosses 

 the sternum from the lower part of the fifth right to the 



' Loc. cit. 



