334 



RESPIRATION. 



angles formed by their articulation with the 

 sternum ; and this difference in the extent of 

 movement in the two portions of the sternum 

 must be still greater before the manubrium and 

 the body of the bone are united by ossific 

 matter.* Though this description of the 

 movements of the sternum in respiration, 

 which is that given by Hallerf, has been 

 called in question by some modern anatomists, 

 there can be no doubt of its correctness, for it 

 can be proved, by an appeal to the mechanism 

 of the thorax, that, in the upward and for- 

 ward movement of this bone, its upper and 

 lower ends will pass through paths which 

 differ considerably in their curvature and 

 direction. J Though Haller was wrong in 

 maintaining that the first rib is almost im- 

 movable in these actions of the thoracic walls, 

 yet there can be as little doubt that Magendie 

 is in error in asserting that this is the most 

 movable of all the ribs ; for however favour- 

 able the nature of its vertebral articulation 

 may be for motion, this is counteracted by the 

 mode in which its cartilage of prolongation is 

 united to the sternum. 



The position and form of the diaphragm is 

 well adapted for enlarging, by its contraction, 

 the vertical diameter of the thorax ; and being 

 placed in the most capacious part of the 

 thorax, even a slight elongation of the vertical 

 diameter there will add considerably to the 

 area of its inner surface. The convex or 

 upper surface of the diaphragm, in its relaxed 

 state, projects upwards on each side of its 

 central or cordiform tendon into the thorax, 

 and is higher anteriorly than posteriorly, and 

 on the right side than on the left. This 

 cordiform tendon is made a fixed point for 

 the arched fibres that run from it to the ribs 

 during their contraction, since it is pulled 

 upon from below and behind by the two crura 

 of the diaphragm, and in front by the short 

 muscular fibres which pass to it from the 

 point of the sternum and the lower edges of 



* During the elevation of the ribs the elastic 

 cartilages of prolongation of the sternal ribs undergo 

 a certain amount of torsion, and the angles they 

 form with the sternum become less acute. The en- 

 largement of the chest produced by the elevation of 

 the ribs is greater in the antero-posterior than in 

 the transverse diameter, and the enlargement in the 

 transverse direction is much greater at the anterior 

 than at the posterior portion of the chest, from the 

 mode in which the ribs are articulated with the 

 vertebral column. 



f Haller (Memoire sur plusieurs Phenomenes 

 Importantes de la Respiration. Lausanne, 1758) 

 found that the upper edge of the sternum was car- 

 ried forwards 2^, and the lower end from 3 to 8 

 lines, in a moderate inspiration. 



1 Ward's Human Osteology, p. 212. 1838. 



The elasticity of the cartilaginous and osseous 

 portions of the walls of the thorax will afford con- 

 siderable resistance to the muscles in dilating it 

 during inspiration. From the results obtained in 

 two experiments upon the chest after death, Dr. 

 Hutchinson calculates (Medico-Chirur. Transact, of 

 London, vol. xxix. p. 205. 1846) that the force 

 which the muscles of inspiration have to overcome 

 in ordinary breathing from this source is probably, 

 at least, equal to about 100 Ibs., and in deep inspi- 

 ration to about 300 Ibs. In these calculations the 

 additional resistance from the elasticity of the lungs 

 was not taken into account. 



the cartilages of the ribs. If the lower ribs 

 have been previously rendered steady by 

 the action of the quadrati lumborum and 

 serrati postici inferiores muscles, the arched 

 muscular fibres of the diaphragm have another 

 fixed point during their contraction. As the 

 heart rests on the upper surface of the cordi- 

 form tendon, and the base of the lungs on 

 the upper portion of the arched part of the 

 diaphragm, the descent of the arched muscular 

 fibres and their change to the horizontal posi- 

 tion, causes a considerable enlargement of 

 that part of the chest occupied by the lungs, 

 while the position of the heart is compara- 

 tively little affected when the respiratory 

 movements are moderate; but during forcible 

 inspiration the heart recedes deeper into the 

 chest, and during expiration it again comes 

 forward. * The vertical diameter of the chest 

 may be increased in inspiration by the pulling 

 up of its superior portion, by the strong 

 muscles of the neck attached to it, at a time 

 when the lower portion is prevented from 

 ascending, but an increase in the vertical dia- 

 meter by an elongation of its upper part 

 must have a much less effect in enlarging its 

 capacity than an elongation of its lower part 

 seeing that the thorax is at least four times 

 as large at its lower as at its upper end. In 

 ordinary respiration, and when the body is at 

 rest, the ribs move little in the male, and the 

 muscular movements of inspiration are chiefly 

 carried on by the diaphragm. -j- 



The ribs are elevated, in ordinary respira- 

 tion, by the levatores costarum, external and 

 internal intercostal muscles J, and also, more 



* In the article HEART, Vol. II. p. 578, in stating 

 this circumstance, the word inspiration was inad- 

 vertently used for expiration, and vice versa. 



f Dr. Hutchinson (Medico-Chirurg. Transact, of 

 London, vol. xxix. p. 187. 1846) by a delicate in- 

 strument measured the costal movement during 

 ordinary respiration in healthy individuals of the 

 male sex, and found it not to exceed from two to 

 four tenths of a line. The costal movements in the 

 female sex, especially at the upper part of the chest, 

 are considerably more extensive. Dr. Hutchinson 

 states that the difference between the circumference 

 of an ordinary man's chest measured over the nipples 

 in the two states of a deep inspiration and a deep 

 expiration, amounts to 3 inches (Opus cit. p. 222) ; 

 and Valentin, under the same circumstances, found 

 the average difference in the circumference of the 

 chest, measured over the scrobiculus cordis, in seven 

 individuals of the male sex between 17 J and 33 

 years of age, to be 1 : 8'29 of the whole circumfer- 

 ence. (Lehrbuch, &c. erster band, S. 541. 1844.) 

 In old age, when the costal cartilages of prolonga- 

 tion become ossified, the mobility of the chest must 

 be diminished. 



J The mode of action of the intercostal muscles 

 has been a subject of discussion since the time of 

 Haller, many entertaining the opinion of Haller, 

 that both the internal and external sets act simul- 

 taneously as muscles of inspiration ; some, that they 

 are muscles of expiration ; while others, again, as- 

 sert that one set act during inspiration, and the 

 other set during expiration. Those who maintain 

 the last opinion are not agreed among themselves 

 as to what set act as muscles of inspiration, and 

 what as muscles of expiration. The mode of action 

 of these muscles has lately been carefully examined 

 by MM. Beau and Maissiat and Mr. Sibson (Opus 

 cit.) ; and the two former (Archives Generates de 

 Medecine, 4 serie, torn. i. p. 268. 1843),; conclude 



