MUSCLES OF INSPIRATION. 123 



called ordinary auxiliaries ; while others, which ordinarily have a different function, are 

 only brought into play when respiration is excessively difficult, and are called extraordi- 

 nary 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 cer- 

 vical 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 ver- 

 tebrae 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 vertebras ribs, between 



the tubercles and angles. 



Ordinary Auxiliaries. 



Serratus posticus superior Ligamentum nuchae, spinous processes of last cervical 



and upper two or three dorsal vertebrae upper bor- 

 ders of second, third, fourth, and fifth ribs, just beyond 

 the angles. 



Sterno-mastoideus Upper part of sternum mastoid process of temporal 



bone. 



Extraordinary Auxiliaries. 



Levator anguli scapulae Transverse processes of upper three or four cervical 



vertebrae posterior border of superior angle of 



scapula. 



Trapezius (superior portion) Ligamentum nuchae and seventh cervical vertebra 



upper border of spine of scapula. 



Pectoralis minor. . Coracoid process of scapula anterior surface and up- 

 per margins of third, fourth, and fifth ribs, near the 

 cartilages. 



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

 er part of sternum. 



Serratus magnus Inner margin of posterior border of scapula external 



surface and upper border of upper eight ribs. 



Action of the Diaphragm. The descriptive and general anatomy of the diaphragm 

 gives a pretty correct idea of its functions in respiration. It arises, anteriorly, from the 

 inner surface of the ensiforrn cartilage, laterally, from the inner surface of the lower 

 borders of the costal cartilages and the six or seven inferior ribs, passes over the quadra- 

 tus lumborum by the external arcuate ligament, and the psoas magnus by the internal 

 arcuate ligament, and has two tendinous slips of origin, called crurae of the diaphragm, 

 from the bodies of the second, third, and fourth lumbar vertebrae and the intervertebral 

 cartilages on the right side, and the second and third lumbar vertebrae and the interver- 

 tebral cartilages on the left side. From this origin, which extends around the lower cir- 

 cumference of the thorax, it 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 some- 



