I046 -> A MANUAL OF ANATOMY 



levatores costarum ; (4) the serratus posticus superior ; (5) the serratus pos- 

 ticus inferior ; and (6) the quadratus lumborum, as being auxiliary to the 

 diaphragm, the serratus posticus inferior being also auxiliary. Ordinary 

 quiet expiration is due to (i) the elastic recoil of the lungs, (2) the elastic 

 recoil of the thoracic wall (costal cartilages and sternum), (3) the triangularis 

 sterni muscle, and (4) the muscles of the antero-lateral wall of the abdomen, 

 which press mildly upon the abdominal viscera, and thereby push the 

 diaphragm upwards towards the thorax. 



In forced inspiration the following muscles come into play : (i) the scaleni ; 

 (2) the sterno-cleido-mastoid ; (3) the serratus magnus ; (4) the pectoralis 

 major and pectoralis minor ; and (5) the latissimus dorsi. As auxiliary muscles 



Fig. 434. — Diagram showing the Axes of Rotation of the Ribs (from 

 Halliburton's 'Handbook of Physiology'). 



A, B, Axis passing from Costo-central to Chondro-sternal Joint ; a, b, Axis 

 passing through Costo-transverse and Costo-central Joints. (The movement 

 round the axis A, B resembles the raising of the handle of a bucket.) 



there are the trapezius, levator anguli scapulae, and rhomboid muscles, which, 

 by their action upon the scapula, fix the shoulder. 



In forced expiration the muscles of the antero-lateral wall of the abdomen 

 act with considerable strength, and now depress those ribs with which they 

 are connected, and necessarily also the sternum. By some authorities the 

 serratus posticus inferior is regarded as being concerned. 



In inspiration the thoracic cavity is enlarged in its vertical, antero-posterior, 

 and transverse diameters. The increase in the vertical diameter is due to the 

 contraction and descent of the diaphragm ; the increase in the antero-posterior 

 diameter is caused by the anterior parts of the ribs, and along with them the 

 sternum, being carried forwards ; and the increase in the transverse diameter 

 is brought about by the eversion of the lower borders of the ribs, and the 

 opening out of the angles between the ribs and their costal cartilages. 



GUIDE TO THE THORAX. 



Thoracic Wall. — The upper limb having been separated from the trunk, 

 the dissector should remove the remains of the following muscles : the pec- 

 toralis major, pectoralis minor, tendon of origin of the subclavius, serratus 

 magnus, obliquus externus abdominis, latissimus dorsi, and rectus abdominis. 

 In removing the remains of the pectoralis major the anterior cutaneous nerves 



