THORAX. 



1033 



times continuous with the sternum, and is 

 sometimes articulated like the cartilages of 

 the other ribs. Cruveilhier found in one sub- 

 ject the 1st rib excessively moveable, because 

 its cartilage, instead of being continuous with 

 the sternum, had its upper edge applied to the 

 side of that bone to which it was united by 

 ligaments, and was ultimately articulated by 

 a narrow extremity immediately above the 

 2nd rib. 



2ndly. The second cartilage is much more 

 angular at its inner extremity than any of the 

 others : it is received into the retreating angle 

 formed by the union of the first, two pieces of 

 the sternum. Sometimes there is an inter- 

 osseous ligament in this joint, running from 

 the angle of the cartilage to the bottom of the 

 cavity, and there are then two synovial cap- 

 sules ; in other cases there is only one, but it 

 is always more marked than in the other 

 joints. 



The articulations of the 6th and 7th carti- 

 lages, besides the anterior ligaments, have also 

 a chondro- or costo-xiphoid ligament, more or 

 less strong, which crosses with the ligament of 

 the opposite side in front of the ensiform car- 

 tilage, and the lower end of the sternum. 

 Sometimes this ligament only exists for the 

 7th cartilage ; it is intended not only to 

 strengthen the chondro-sternal articulation, 

 but also to maintain the xiphoid appendix in 

 its place. 



Connection of the ribs with their cartilages. 

 The cartilages are almost immovably 

 united to the ribs, being received into rounded 

 depressions on the ends of the ribs, and their 

 union is maintained only by periosteum, which 

 may be considered to represent their liga- 

 ments. 



Articulations of the costal cartilages one with 

 the other. Some of the costal cartilages 

 articulate with each other by their edges. 



The 1st, 2nd, 3rd, 4th, and 5th costal car- 

 tilages do not articulate together, unless the 

 aponeurotic lamellae, sometimes very strong, 

 which form the continuation of the external 

 intercostal muscles, and occupy the whole 

 length of the cartilages, be considered as 

 uniting media. 



The 6th, 7th, and 8th cartilages, frequently 

 the 5th, and sometimes the 9th, present true 

 articulations with one another. Cartilaginous 

 processes arise from the neighbouring edges 

 and come in contact with each other : there 

 are sometimes two articular faces between the 

 6th and 7th cartilages. The means of union 

 are some vertical fibres united in bundles, so 

 as to form two ligaments, the one anterior 

 and thicker, the other posterior and thinner. 

 The edges of the articulating surfaces, from 

 the 6th to the 8th or 9th, are lined by sy- 

 novial membrane. The 7th, 8th, and 10th 

 cartilages have not always articular surfaces, 

 but are simply united by vertical ligaments. 



Ligaments of the sternum {Membranes sterni, 

 Weitbr.). The pieces of the sternum are 

 connected by a layer of fibro-cartilage, 

 placed between their contiguous borders ; and, 

 on the anterior and posterior surfaces, liga- 



mentous fibres maybe observed running longi- 

 tudinally, which serve to strengthen their con- 

 nection. They are sometimes called the 

 anterior and posterior sternal ligaments. The 

 longitudinal fibres are mixed with those ra- 

 diating from the costal cartilages, especially 

 in front of the sternum, where likewise they 

 blend with the aponeurosis of the pectoral 

 muscles. The anterior portion has thus most 

 of the accessory fibres, and is rough and irre- 

 gular ; the posterior one is smooth and pearly 

 in its aspect. 



The muscles of the thorax will be more con- 

 veniently noticed hereafter. 



OF THE THORAX IN GENERAL. The ster- 

 num, the ribs and their cartilages, together 

 with the dorsal vertebrae, are so united to- 

 gether as to compose the frame-work of the 

 thorax. (Jig. 662.) Their arrangement is such 

 as collectively to admit of great mobility, and 

 at the same time to protect completely the or- 

 gans of respiration and the heart. How well 

 adapted this mechanism is for protecting those 

 vital organs is well shown by the impunity 

 with which the prize-fighter receives for many 

 hours the trained blows of his antagonist. 



Although the range of motion between each 

 vertebra and the ribs attached to it, is very 

 limited, yet the whole frame-work of the 

 chest enjoys such mobility, that, by a deep 

 inspiration, its capacity is sometimes more 

 than doubled. This bony frame-work is by 

 no means destined solely to cover the respira- 

 tory organs, for it extends considerably down- 

 wards, composing part of the abdominal walls 

 within which lie the liver, spleen, kidneys, 

 stomach, duodenum, and part of the colon ; 

 hence the distinction between thoracic and 

 diaphragmatic ribs. In fact it will be found 

 that about one half only of the costal surface 

 is destined to compose the thorax. The shade 

 running transversely across the ribs in^g. 632. 

 marks the bottom of the thoracic cavity. 



In each individual the thoracic cavity cor- 

 responds exactly with the volume of the heart 

 and lungs. But there is no relation between 

 the volume of the lungs and the vigour of the 

 constitution nor between the size of the ca- 

 vity of the thorax and the amount of air which 

 can be respired, as will be hereafter shown. 

 There is likewise no relation between the vo- 

 lume of the thorax and that of the abdominal 

 cavity. No doubt the vigour of aeration in the 

 lungs is at all times exactly commensurate with 

 the vigour of the alimentary canal, so that the 

 one harmonises with the other; but this vigour 

 bears no relation to space or size. A small 

 thorax may in some individuals admit of 

 the inspiration of a greater volume of air 

 than a larger thorax in others. In fact it 

 may be commonly noticed that where there 

 is a large abdomen there is generally a 

 small thorax, and that the volume of air 

 which can be expelled at one effort from the 

 lungs of those who have a large abdomen, 

 is less than from those with a small abdomen. 

 The alimentary canal receives at once a given 

 quantity of food, and there it remains for an 

 indefinite time, the thorax large o- small, it 



