MUSCLES OF INSPIRATION 97 



narily have different uses, act only when respiration is difficult, and are 

 called extraordinary auxiliaries. 



The following are the principal muscles concerned in inspiration : 



MUSCLES OF INSPIRATION 



Ordinary Respiration 



MUSCLE ATTACHMENTS 



Diaphragm Circumference of lower border of thorax. 



Scalenus anticus ......... Transverse processes of third, fourth, fifth and sixth 



cervical vertebrae tubercle of first rib. 

 Scalenus medius Transverse processes of lower six cervical vertebrae 



upper surface of first rib. 



Scalenus posticus Transverse processes of lower two or three cervical 



vertebrae outer surface of second rib. 



External intercostals Outer borders of the ribs. 



Sternal portion of internal intercostals . . Borders of the costal cartilages. 



Twelve levatores costarum Transverse processes of dorsal vertebrae ribs, be- 

 tween the tubercles and angles. 



Ordinary Auxiliaries 



Serratus posticus superior Ligamentum nuchae, spinous processes of last cer- 

 vical and upper two or three dorsal vertebrae 

 upper borders of second, third, fourth and fifth 

 ribs, just beyond the angles. 



Sterno-mastoideus Upper part of sternum mastoid process of tem- 

 poral bone. 



Extraordinary Auxiliaries 



Levator anguli scapulae Transverse processes of upper three or four cer- 

 vical vertebrae posterior border of superior 

 angle of scapula. 



Trapezius (superior portion) v Ligamentum nuchae and seventh cervical vertebra 



upper border of spine of scapula. 

 Pectoralis minor Coracoid process of scapula anterior surface and 



upper margins of third, fourth and fifth ribs, near 

 the cartilages. 



Pectoralis major (inferior portion) . . . Bicipital groove of humerus costal cartilages and 



lower part of sternum. 



Serratus magn us Inner margin of posterior border of scapula exter- 

 nal surface and upper border of upper eight ribs. 



Action of the Diaphragm. The descriptive and general anatomy of 

 the diaphragm gives an idea of its uses in respiration. It arises from 

 the border of the lower circumference of the thorax and mounts into the 

 cavity of the chest, forming a vaulted arch, or dome, with its concavity 

 toward the abdomen and its convexity toward the lungs. In the central 

 portion, there is a tendon of considerable size and shaped something 

 like the club on a playing-card, with middle, right and left leaflets. The 

 rest of the diaphragm is composed of radiating fibres of striated muscular 

 tissue. The oesophagus, aorta and inferior vena cava pass through the 

 diaphragm from the thoracic to the abdominal cavity, by three openings. 



