374 RESPIRATION. 



late elaborate work assumes that the question is still left in 

 considerable uncertainty. 1 The most elaborate researches on 

 this point are those of Beau and Maissiat (Archives Generates 

 de Medecme, 1843), arid Sibson (Philosophical Transactions, 

 1846). The latter seem to settle the question of the mode of 

 action of the intercostals, and explain satisfactorily certain 

 points which even now are not generally appreciated. 3 



Let us first note the changes which take place in the 

 direction of the ribs, and their relation to each other, in 

 inspiration, before considering the way in which these move- 

 ments are produced. 



In the dorsal region, the spinal column forms an arch 

 with its concavity toward the chest, and the ribs increase in 

 length progressively, from above downwards, to the deepest 

 portion of the arch, where they are longest, and then become 

 progressively shorter. " During inspiration the ribs approach 

 to or recede from each other according to the part of the arch 

 with which they articulate ; the four superior ribs approach 

 each other anteriorly and recede from each other posteriorly ; 

 the fourth and fifth ribs, and the intermediate set (sixth, 

 seventh, and eighth), move further apart to a moderate, the 

 diaphragmatic set (four inferior), to a great extent. The upper 

 edge of each of these ribs' glides toward the vertebrae in rela- 

 tion to the lower edge of the rib above, with the exception of 

 the lowest rib, which is stationary." s 



These movements, accurately and admirably described 

 by Sibson, and illustrated by drawings of the chest, empty, 



1 LONGET, Traite de Physiologic, Pari?, 1861, tome i., p. 629. 



a Sibson's article is the most complete ever published upon the mechanism of 

 respiration. The action of the respiratory muscles was observed in vivisections, 

 and the mechanism by which the capacity of the thorax is modified is illustrated 

 in the most ingenious manner by mechanical contrivances, representing the posi- 

 tion, etc., of the ribs, and their movements. By dilating the chest after death, 

 also, he shows the change which takes place in the direction of the ribs and the 

 consequent shortening of certain muscles, which, he assumes, must act as muscles 

 of inspiration, a fact which he has taken care to verify by vivisections. 

 * SIBSON, op. cit., p. 629. 



