1048 A MANUAL OF ANATOMY 



out. On both sides the anterior intercostal aponeuroses and interchondral 

 fibres of the internal intercostal muscles should be removed. The internal 

 mammary artery and its branches, along with its venae comites, and the 

 anterior intercostal or sternal glands are then to be dissected. The artery 

 will be found about ^ inch from the side of the sternum, and its superior 

 phrenic branch (comes nervi phrenici) is to be preserved until a later period. 

 The venae comites are also to be subsequently shown uniting superiorly to 

 form one vessel. In the sixth intercostal space the internal mammary 

 artery is to be shown dividing into its two terminal branches, namely, mus- 

 culo-phrenic and superior epigastric. The triangularis sterni muscle is then 

 to be dissected from before. On the side on which the costal cartilages have 

 been left intact they are now\ to be cut through from the second to the sixth 

 inclusive, close to the osseous ribs. Thereafter the ribs corresponding to 

 these costal cartilages on each side are to be divided with the bone-forceps, 

 and this should be done as far back as possible by turning the subject round 

 on either side. The divided ribs are then to be bent backwards, the parietal 

 pleura having been carefully separated from them. The sternum, meanwhile, 

 is to be left undisturbed, with whatever costal cartilages are attached to it. 

 The parietal pleura is then to be carefully studied. By way of showing that 

 it does not descend as low as the lins of attachment of the diaphragm, the 

 external and internal intercostal muscles of one or two of the lowest spaces 

 should be removed, when it will be seen that the diaphragm comes into view 

 without any trace of parietal pleura. 



The manubrium sterni is next to be partially sawn through near its lower 

 border, the seventh costal cartilage on each side is to be cut through, and 

 the great bulk of the sternum is then to be bent upwards in such a manner 

 that it can be replaced when required. If the bone should break, the two 

 parts should be connected by wire sutures. The relations of the anterior 

 borders of the two pleural sacs to the sternum, to each other, and to the 

 pericardium, are now to be carefully studied. The anterior mediastinum 

 and the remains of the thymus body are to be inspected, and the area of the 

 pericardium which is uncovered by the left pleura, and is directly related 

 to the thoracic wall, is to receive special attention. 



At this stage an opening should be made in the cervical portion of the 

 trachea, and a blow-pipe, provided with a stop-cock, should be introduced 

 and tied firmly in position. The lungs are now to be inflated through the 

 blow-pipe, the stop-cock is to be turned, and the following points are to be 

 accurately observed : (i) the extent to which the lungs encroach upon the 

 heart, enclosed within the pericardium ; and (2) the extent to which they 

 descend between the diaphragm and the ribs. By reversing the stop-cock 

 the lungs will be seen to collapse and recede from the precordial area. During 

 these observations the greater part of the sternum should be alternately 

 raised and lowered. 



The chief part of the sternum is now to be removed, along with whatever 

 costal cartilages are connected with it. On the side on which the cartilages 

 remain in connection with the bone the triangularis sterni and the internal 

 mammary vessels are to be dissected from behind. The chondro-sternal 

 joints may be dissected at this stage, or it may be convenient to preserve 

 the sternum for their future dissection. 



Phrenic Nerves, Pleurae, Pericardium, and Lungs. — Before the further stages 

 of the dissection are entered upon, it is necessary that the dissector should 

 have some knowledge of the general position of the structures to be exposed. 

 From their complicated nature it is not possible to lay down hard-and-fast 

 directions, and in his mode of procedure he must keep a careful look-out. 



The phrenic nerve is to be dissected, and its close relation to the pericardium 

 is to be noted, as well as its course in front of the root of the lung. Possibly 

 the superior phrenic branch (comes nervi phrenici) of the internal mammary 

 artery may be found coming into contact with the nerve high up in the thorax. 

 The reflections of the pleura are to be studied both in the transverse and 

 in the vertical directions. If any adhesions are present, these should be 

 separated with the fingers, and any fluid which has accumulated must be 



