1031 



THORAX. 



matters not which, aerates the blood from this 

 food by movements, quick or slow, long or 

 short ; therefore the respiratory movements 

 only, need be relative to the abdominal cavity, 

 in the same way as the volume of the blast 

 from a pair of bellows is more dependent on 

 their mobility than on their absolute size. The 

 above remarks are applicable to the thorax 

 of either male or female. 



I. Boundaries of the thoracic cavity. The 

 thoracic cavity, situated between the shoul- 

 ders and below the neck, extends but a 

 short way downwards, in the male about seven 

 inches, and in the female about eight inches, 

 below the clavicle, so that a horizontal line 

 drawn about an inch below the axilla, corres- 

 ponds (roughly) with its floor. The floor of 

 the chest, therefore, is much higher up in the 

 trunk of the body than is commonly supposed. 

 The thorax is bounded anteriorly by the 

 sternum and costal cartilages ; laterally by the 

 bodies of the ribs and the intercostal muscles ; 

 posteriorly by the vertebrae and angles of 

 the ribs, and inferiorly by a thin tendinous 

 and fleshy floor the diaphragm. The su- 

 rior aperture of the chest is about sixteen 

 inches in circumference, this is the smaller 

 end, and thence called the apex of the tho- 

 rax. It is bounded laterally by the two 1st 

 ribs, anteriorly by the upper edge of the 

 sternum and inter-articular ligament, and 

 posteriorly by the last cervical and first dorsal 

 vertebrae. The inferior aperture is about 

 thirty or thirty-one inches in circumference, 

 and forms the base of the chest. Anatomists 

 describe this part as bounded in front by 

 the cartilaginous extremity of the sternum 

 or xiphoid cartilage, and the cartilaginous 

 extremities of the last true and false ribs, and 

 more laterally by the 1 1th and 12th ribs, pos- 

 teriorly by the last dorsal and first lumbar 

 vertebrae. But as they assume to themselves 

 the privilege of giving a bone' a surgical neck as 

 well as an anatomical one, so may we take a 

 similar liberty in describing the thorax for 

 medical purposes. In the examination of the 

 chest during life, too exclusive attention to 

 anatomical boundary has probably led to the 

 error, of regarding the chest as much deeper 

 than it really is, and thence to examining for 

 disease of the lung where really little or no lung 

 exists. A sharp instrument, piercing the chest 

 laterally, at the cartilaginous extremities _of 

 the last true ribs, would most probably pene- 

 trate no lung, for the liver, spleen, stomach, &c. 

 are contained within these points. The 

 bottom of the chest is so moveable and so 

 much arched (See art. DIAPHRAGM, /g. 3.), 

 that in the different stages of inspiration, the 

 lung assumes different positions This may be 

 demonstrated by percussing over the 5th rib 

 at its junction with its cartilage, first after a 

 deep expiration and then after a deep inspira- 

 tion ; in the latter the sound is " clear," in 

 the former it is strikingly " dull." Therefore, 

 instead of taking the insertion of the dia- 

 phragm as the bottom of the thorax, it will be 

 found more convenient for examining the 

 chest to take the top of the arch of this muscle 



as the lower thoracic boundary, or the shaded 

 line crossing the ribs in fig. 4., for the medical 

 base. This may be described as corres- 

 ponding in front with the xiphoid cartilage ; 

 laterally to different osseous portions of the 7th, 

 8th, 9th, 10th, llth, and sometimes the 12th 

 rib (fig. G82.), and posteriorly to the 8th and 

 9th dorsal vertebras. This will place the 

 bottom of the thorax in a very different posi- 

 tion from what is generally supposed ; for, if 

 we express the distance from the 1st rib, to 

 the lowest point of the 10th rib as ]3'5, that 

 from the 1st rib to the arch of the diaphragm 

 or medical boundary will be only G'25, less 

 than one half the depth of the thorax as ana- 

 tomically described. The medical base of the 

 thorax forms a nearly horizontal plane, which 

 extends between the sternum and the bo- 

 dies of the 9th or 10th dorsal vertebrae, its 

 posterior being somewhat higher than its an- 

 terior. But on each side of the bodies of the 

 vertebrae there is a deep groove formed by the 

 angles of the ribs. In that part of this groove 

 which extends below the above-mentioned in- 

 clined plane, a wedge-shaped process of lung 

 is lodged, which varies in size in different sub- 

 jects, and consequently will be found to ter- 

 minate at different points in the dorsal re- 

 gion, as already noticed, sometimes hanging 

 down like a broad, thick flap, and at other 

 times forming only an insignificant process. 



In examining the chest, it is of paramount 

 importance that the student should familiarly 

 know this medical fioor of the thorax. The 

 sign laid down by the late Dr. Edwyn Har- 

 rison, for marking this boundary, we have 

 found strictly correct in every normal-shaped 

 thorax. Namely, take the xiphoid cartilage as 

 a point to start from, and pass the fiat hand 

 horizontally from thence to the side of the 

 chest, the index finger, when horizontal, will 

 distinguish a slight depression or sulcus at the 

 maximum lateral bulge of the thorax, then 

 from this point slide the hand slightly upwards 

 (perpendicularly), and it will pass over a 

 bulge, about enough to fill the palm of the 

 hand, into another sulcus, better defined than 

 the former one ; this groove corresponds with 

 the medical base of the thorax, and a probe 

 passed in here would graze the arch of the 

 diaphragm after passing through the moveable 

 inferior edges of the lungs. It is necessary that 

 the hand be kept perfectly horizontal, or it 

 will fall into an intercostal space, which does 

 not correspond with the groove in question. 

 With practice, the hand falls at once into the 

 upper sulcus, without first searching for the 

 lower one ; indeed, latterly, Dr. Harrison 

 allowed that the lower sulcus might be absent, 

 and yet the upper one present. 



This groove is higher upon the right side 

 than upon the left, corresponding to the height 

 of the liver. 



By external observation, the medical base of 

 the thorax may be known by the slight rota- 

 tory motion made upon the diaphragm when 

 a person is walking. A kind of great ball 

 and socket-joint may be conceived to exist 

 between the abdomen and thorax, and the 



