NEW VIEW OF THE MECHANISM OF RESPIRATION 295 



Professor Flint has given expression to the views of the majority of physiologists of the present day, and is in no 

 way to be held responsible for popular beUefs however incorrect. 



For these and other reasons already stated, I hold that the inspiratory and expiratory muscular movements are 

 both vital in their nature, and that the abdominal muscles of expiration are correlated to, and act in concert with, 

 the thoracic muscles of inspiration. 



The inspiratory and expiratory movements are produced by spontaneous self-acting muscles ; elasticity playing 

 quite a subordinate part in both movements, but being most pronounced in expiration. 



As regards the subject of elasticity it may be well to point out that the elastic properties of living muscles and 

 elastic bodies generally, such as steel, caoutchouc, and other springs, are not identical, and give quite different 

 results. The elasticity of muscle acts slowly and is more or less under control — that of mechanical springs acts 

 quickly and is, in no sense, under guidance. 



While I do not attach the same importance to elasticity in muscular action as some of my confreres do, I 

 am far from denying its existence or ignoring its power in animal physics. It certainly does perform a" useful function 

 in expiration and in wing and other movements. 



The one-sided view of the opening and closing of the chest, whereby the opening is ascribed to vital action 

 inhering in the muscles, and the closing to elastic recoil, is due to the almost universal belief that muscle is endowed 

 with only one power, namely, that of shortening or contracting. A compensating force in that case becomes a 

 necessity, and elasticity is made to do duty in and out of season when a difficulty arises. For reasons already 

 stated, I maintain that muscles are endowed with a double power, namely, a centripetal power of contracting 

 or shortening, and a centrifugal power of relaxing or elongating ; these movements being both vital in their 

 nature. An analysis of the movements of muscle (voluntary and involuntary) is given in Sections 54 and 55 of the 

 present work. 



According to my views, muscles never oppose and contend against each other as rivals. On the contrary, 

 they work harmoniously together ; elasticity helping them over their dead points and contributing to the continuity 

 of their movements. 



Hitherto I have confined my observations to the movements of the respiratory muscles m calm or normal 

 breathing, and before leaving the subject, and in order to emphasise my findings on an avowedly difficult and important 

 matter, I append a table in which not only the muscles engaged are enumerated, but also their attachments set forth. 

 The nmscles connected with violent or forced breathing are given further on. They are usually designated extra- 

 ordinary muscles of respiration. 



TABLE OF MUSCLES ENGAGED IN RESPIRATION ACCORDING 



TO THE AUTHOR 



Inspiratory Muscles Engaged in Ordinary Calm Breathing 



Aitarhiiiimfx. 



(a) The external and internal intercostal The external intercostal muscles are attached to the outer borders of 

 muscles. the ribs ; the internal intercostal muscles (sturnal portions) to the 



borders of tlic costal cartilages. 



(6) The pectorales minor muscles.' These muscles are attached to the coracoid process of the scapula and 



the anterior surfaces and upper margins of the third, foiu'th, and fifth 

 riljs near the cartilages. 



(c) The soaleni muscles (anticus, medius, and The scalenus anticus muscle is attached to the third, fourth, and fifth 



posticus). ribs of the c('r\-ical vertebrse and the tubercle of the tii'.st rib ; the 



scalenus medius to the transverse processes of the lower six cevvii.'al 

 vc'T'tebviE and the upper surface of the first rib ; the scalenus posticus 

 to the transverse processes of the lower tliree cervical vertebrse and the 

 outer surface of the second rib. 



(d) The twelve levatores costarum muscles. The levatores costarum muscles are attached to the transverse processes 



of the dorsal vertebrse and the ribs liet ween the tubercles and angles. 



(e) The diaphragm, at once inspiratory and ex.- The diaphragm is attached to the bodies of several of the upper lumbar 



piratory. vertebrfe, the ligamenlum ai'cuata, the ensiform cartilage, and the carti- 



lages of the sixth lower rilis. 



' These muscles are said to net in forced or deep inspiration. 



