410 



PHYSIOLOGY 



CHAP. 



contraction of its muscular fibres, which converge towards the 

 trilobate tendinous centre, the convexity towards the thoracic 

 cavity diminishes, pushing the abdominal viscera downwards. 

 According to Hasse (1880), during maximal inspiration the right 

 lobe of the tendinous centre descends 2'5 cm., the left lobe 2 cm., 

 and the central lobe about 1 cm. The muscle fibres inserted in 

 the cartilages of the six last ribs contribute to the elevation and 



expansion of the lower ribs, 

 since they are directed almost 

 vertically upwards, the vault 

 of the diaphragm being sup- 

 ported by the abdominal 

 viscera (Duchenne). The an- 

 terior muscle fibres, which run 

 more horizontally towards 

 the tendinous centre, oppose 

 a certain resistance to the 

 forward displacement of the 

 sternum. This may be the 

 reason why the sternum is 

 bent in patients who have 

 suffered a long time from 

 asthma (Thane). Nor is the 

 action of the diaphragm con- 

 fined to increasing the vertical 

 diameter of the thorax with 

 inspiration, as all admit. It 

 also (by aiding the elevation 

 and expansion of the false ribs) 



Fin. iW.-Deei, and prevortebral muscles of neck. aSSlstS the dilatation of the 



(Allen Thomson.) a, Superficial section of basilar transverse diameter of thebaSC 

 process ; b, transverse process of atlas; <, p , , , -, j j-r> ,v 



transverse process of 7th cervical vertebra ; d, d', OI the tnorax, and modifies tllG 



bodies of 1st and 4th dorsal vertebra; e, c', 1st omWIifipafinTi n f j-V, aon-iffo! 



and 2nd ribs ; 1,2, rectus capitis anterior major amplification OI tne Sagittal 



and minor; 3, 8', 3", median upper and lower diameter at the level of the 

 part of musculus lon^us colli ; 4, 4', 4", >I. 



intertransversales ; 5, y scalenus anterior and its lower CllQ 01 the Sternum, 

 insertion on 1st rib; 6, 6' scalenus medius, and w j i~ i i 11 



insertion on 2nd rib; V, scalenus posterior; 8, effects which are leSS Well 



posterior part of levator scapulae ; !>, splenius k nown an( J are usually OV6r- 



looked. 



Other inspiratory muscles are the_ three i scaleni (Fig. 176), 

 which exert traction on the first two ribs, and Thus elevate and 

 maintain the entire thoracic wall (Duchenne). 



The M. levatores costarurn longi et breves, twelve on each side, 

 are able from their insertion in the immediate vicinity of the 

 costo-vertebral articulations to produce an extensive elevation 

 in the anterior ends of the ribs on gentle contraction (Traube, 

 Kosenthal). The inspiratory action of the M. serratus posticus 

 superior is also evident. 



