446 



DISSECTION OF THE THOEAX. 



Thymus 

 body in 

 foetus : 



size 



The THYMUS GLAND is an organ which is most developed in the 

 infant, and the use of which is not understood. It is placed mainly 

 in the upper part of the thorax ; and it may be best examined in a 

 fulLgrown foetus. 



At birth it is about two inches in length, and of a greyish 

 colour. It consists of two lobes of a conical form, which touch each 

 and extent, other. Its upper end is pointed, and extends on the trachea as high 

 as the thyroid body ; and the lower, wider, part reaches as far as 

 the fourth rib. In the thorax it rests on the aortic arch and its 

 large branches, on the left innominate vein and on the pericardium. 



In the young adult all that remains of the thymus is a brownish 

 rather firm material in the interpleural space behind the upper end 

 of the sternum ; and after middle life it has generally disappeared 

 altogether. 



Remains in 

 adult. 



RELATIONS OF THE LUNGS. 



Number 

 and use. 



Form 



and parts. 



touches 

 diaphragm 



shape and 

 level. 



Apex is in 

 the neck. 



Anterior 

 edge is thin 



position on 

 right, 

 and left 

 side. 



The lungs are two in number, and are contained in the cavity of 

 the thorax, one on each side of the spinal column. In these organs 

 the blood is changed in respiration. 



Each lung is of a somewhat conical form, and takes its shape from 

 the space in which it is lodged. It is unattached, except at the 

 inner side where the vessels enter forming the root ; and it is 

 covered by the bag of the pleura. It has a base and apex, two . 

 borders and two surfaces. Two fissures on the right and one on 

 the left divide it into lobes. 



The base of the lung is hollowed in the centre and thin at the 

 circumference, fitting the convexity of the diaphragm. Following 

 the shape of that muscle, it is sloped obliquely from before back- 

 wards, and reaches in consequence much lower behind than in front. 



Surface marking (fig. 162). The position of the lower border with 

 respect to the wall of the thorax may be roughly indicated by a line 

 drawn from the sixth chondro-sternal articulation with a slight 

 convexity downwards to the tenth dorsal spine ; but it will be 

 slightly lower in front on the left, than on the right side. The apex 

 is rounded, and projects from one to two inches above the anterior 

 end of the first rib, where it lies beneath the clavicle, the anterior 

 scalenus muscle, and the subclavian artery. 



The anterior border is thin, and overlies in part the pericardium. 

 On the right side it lies along the middle of the sternum as low as 

 the sixth costal cartilage. On the left side, however, it reaches, like 

 the pleura, along the middle line only as low as the fourth costal 

 cartilage. Below that spot it presents a V-shaped notch the apex 

 of which is opposite the outer part of the cartilage of the fifth rib. 

 Below the notch the lung extends inwards behind the outer part of 

 the sixth costal cartilage, and the lower border passes round the 

 chest, on the left as well as on the right sides, crossing the seventh 

 rib in the lateral line and the ninth rib when it is half way round 

 the body, and it is roughly at that part a rib and an intercostal space 

 above the line of pleural reflection. 



