180 ANTHROPOLOGY. 



being performed by the small bronchial arteries which proceed directly 

 from the aorta, and from independent plexuses in the lungs which yet com- 

 municate with those of the pulmonary artery. The returning bronchial 

 veins, too, lead partly to the superior vena cava and partly to the pulmonary 

 veins, so that there is always a small quantity of black blood mixed with 

 the arterial in the left auricle. The nerves destined to the lungs pro- 

 ceed from the vagus and sympathetic. The lungs have comparatively 

 little sensibility, as even in extensive pulmonary diseases but little pain is 

 felt. 



PI. 130, fig. 4, larynx, trachea, pericardium, and lungs, from before : 

 ', larynx ; *, trachea ; '• ", lungs ; \ pericardium ; ', superior vena cava ; 

 \ arteria innominata ; ', left carotid artery ; ", left subclavian artery. 



The organs contained within the thoracic cavity are inclosed by three 

 completely closed serous sacs, the two pleuras and the pericardium. The 

 latter has already been described with the heart. Each pleura is a short 

 sac of a conical shape, and contains only the serous vapor it exhales ; 

 although the lung appears within the cavity, it is really external to it or 

 behind it. That portion of each which invests the lungs is called pleura 

 pulmojialis, that connected with the parietes of the thorax being the pleura 

 costalis or parieialis. The relations of the lungs to the pleura may be better 

 understood by supposing the latter at first to occupy the thorax exclusively. 

 They will then constitute two bags, in contact with each other by their 

 inner and opposed faces. If now the lungs are considered to be developed 

 on the outside of the opposed surfaces of each bag, they will force this out 

 towards the exterior, and finally connect each bag into two contiguous 

 lamina; in contact with each other, the one the costal and the other the 

 pulmonary pleura. The small space left anteriorly and posterior to the 

 sternum is called the anterior mediastinum ; that posterior and in front of 

 the vertebrae is the posterior mediastinum. The space between the two, 

 the middle mediastinum^ contains the lungs and heart. The anterior medias- 

 tinum is wider superiorly and inferiorly than in the centre, and is somewhat 

 X-shaped ; the superior portion contains the origin of the sterno-hyoid and 

 thyroid muscles, and the remains of the thymus gland. The posterior 

 mediastinum is longer than the anterior, and includes the oesophagus, the 

 larger blood-vessels, and the thoracic duct. 



PL 130, fig. 3, cross-section of the thorax to exhibit the course of the 

 pleurae : ', heart within its pericardium ; "■ ', substance of the lungs ; \ right 

 pleura arising from the ribs and their cartilages ; it bends back along the 

 sternum, leaves the anterior mediastinum, °, between it and the left pleura, 

 passes over the pericardium, embraces the pulmonary vessels, passes over 

 the lung, bends back again posteriorly, ', the posterior mediastinum being 

 formed between it and the left pleura as before. 



1. The Thyroid Body or Gland is a large, soft, red mass, of a crescentic 

 shape, and lying on the trachea and sides of the larynx. It consists of two 

 large pyramidal portions, called lateral lobes, connected by a narrow slip, 

 the middle lobe or isthmus. The thyroid body is surrounded by a fine tissue ; 

 it is of a soft spongy texture, the cells containing a yellow fluid. Four 

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