ANATOMY. 



onr; iy of HESPIHITIOV 



As these are contained in the cavity of 

 the. thorax, \vc shall consider the subject 

 in the form of a description of that cavity 

 and its eon' 



The ravity of the thorax is the space 

 included by the dorsal vertebrae behind, 

 by the ribs with their cartilages, tl 

 myn, and intercostal muscles, at the sides 

 and fore part; and by the diaphragm be- 

 - Tins cavity is lined by a membrane 

 ;d the pleura, which has a smooth in- 

 surface, constantly moistened by a 

 serous exhalation. 



cavity of the chest contains two 

 Ntmct membranous bags, called the 

 right and left bags of the pleura; each 

 of tlu-se holds the lung of its own side, 

 and is entirely separated from the oppo. 

 site one. The pleura not only forms a 

 Mch holds the lung, but is also re- 

 the surface of the viscus, be- 

 , on it a smooth exterior invest- 

 ment. This is called the pleura pulmo- 

 :ilis, to distinguish it from the other, 



'i is named pleura costalis. 

 I/' the cartilages of the ribs be divided 

 on one side of the chest, the correspond- 

 ing bag of the pleura will be opened ; and 

 it will then appear, that this is separated 

 from the opposite one by a partition, which, 

 extends from the sternum in front to the 

 vertebra behind, and is known by the 

 name of mediastinum. The pleura may 

 be compared to two bladders placed late"- 

 rally with respect to each other, but adher- 

 ing only partially, and separated by vari- 

 ous intervening bodies. Thus, the" heart 

 and adjoining large blood-vessels, the 

 oesophagus, and the division of the trachea 

 into the two bronchi, are placed between 

 the two pleurz. The mediastinum then 

 is the space included between the opposed 

 surfaces of the two bags of the pleunc, 

 and containing the parts above mentioned. 

 ;;()! mediastinum is ap- 

 plied to a small interval left between the 

 two pleune, just behind the sternum, and 

 occupi . loose cellular tt 



The posterior mediastinum 



a front of the bodies of the verte- 

 brae; it containsthe descending aorta, the 

 vena axygos, thoracic duct, oesophagus, 

 and the par vagum. 



The capacity of the chest taken altoge- 

 ther varies, according as we estimate it in 

 a state of inspiration or expiration; being 

 largest in the former, and smallest in the 

 tate. The right bag of the pleura 

 is considerably larger than the left, as i 

 also the rightJungv 



In ^the living state, the lung is in close 

 contact with the surface of the IMUU, and 

 follows all the motions of the sidi s of the 

 chest, [t is distended by the inH 

 when the chest is enlarged ; and the air is 

 expelled from tile lung, when 'die chest is 

 diminished. As soon as tile thorax is 

 opened in the dead subject, the lung falls 

 down from the sides of the chest, or, in 

 technical language, collapses, and then a 

 large empty space is seen between it and 

 the ribs. From this representation it 

 should appear, that the iungs are quite 

 passive in the business of respiration. 



The lungs axe two in number: one be- 

 ing contained in each bag of the pleura. 

 They are loose and unconnected in these 

 bags, excejtat one point, towards the up- 

 per and posterior portion of each 

 where the great vessels enter them, and 

 where the bag of the pleura is continu- 

 ous with the reflected portion of the mem- 

 brane. These are called the ligaments of 

 the lungs. 



Their colour varies considerably. It is 

 always verging more to a red, in propor- 

 tionasthe subject isyonnger: in the adult, 

 it has more of a spotted and livid cast. 

 Towards the back of the lungs it '. . always 

 much deeper,from the gravitation of blood 

 in the vessels in consequence of the posi- 

 tion of the subject. It is lighter, when the 

 lungs contain much air. 



The lungs are subdivided into lobea ; 

 of which the rightcontains three, and the 

 left two. Their substance is composed of 

 a congeries of minute membranous cells, 

 about equal in size to a pin's head, and as 

 these are more or less filled with air, they 

 give the lung a peculiar spongy feel. 

 These ceils communicate with the ulti- 

 mate ramifactions of the air vessels, and 

 air from that source. The pul- 

 monary vessels ramify minutely in them, 

 expose the blood" to the ef- 

 fects of the contained air ; and in this ex- 

 posure the object of respiration is eilectcd. 

 The -windpipe. The tube, which con- 

 veys the external air into the lungs, n.ay 

 be divided into three pans ; the i. 



hea, and the bronchi. 

 The larynx is a hollow cartilaginous or- 

 gan, place'd at the top of the trachea. The 

 air which passes through this from the 



:i expiration, produces the voice. 

 The cavity of the larynx opens above at 

 the root of the tongue, and below into the 

 trachea. The organ is composed of five 

 : \i/.. tlie thyroid and 

 cricoid cartilages and epiglottis, and two 

 arytenoid cartilages. 



The thyroid cartilage is the largest, and 



