124 



HITCHCOCK'S ANATOMY 



the arm downwards and backwards, as in the movements of 

 chopping wood or striking with the blacksmith's sledge. But 

 when the hands are made the fixed points, the body is raised 

 upwards. 



248. Superior and Inferior Serrati. — Two muscles of the 

 back are used in forced or violent respiration. These are the 

 Superior and Inferior Serrati Muscles. The Superior Ser- 

 ratus arises from the three lower cervical and two upper dorsal 

 vertebrae, and runs downwards and forwards to be inserted 

 into the border of the second, third, and fourth ribs. The 

 Inferior Serratus arises from the last two dorsal and three 

 upper lumbar vertebrae, and, running upwards and forwards, 

 is inserted upon the four lower ribs. The name of these mus- 

 cles means in Latin " saw-like," since the portions which join 

 upon the ribs resemble the teeth of a saw. The former of 

 these elevates the ribs, thereby enlarging the cavity of the 

 chest, while the latter assists in its compression by depressing 

 the ribs, and consequently the diaphragm, downwards. 



249. The Diaphragm —But the essential muscle of respi- 

 ration is the Diaphragm. This, as its name implies, is a par- 

 tition across the body just below the lungji, — with three 

 large openings, — which separates the thorax from the abdo- 

 men. Its attachments in general terms may be said to be 

 upon an oblique line drawn about the body just below the 

 ribs, which line intersects the first lumbar vertebra, where 

 the central tendon of the Diaphragm, as it is termed, is at- 

 tached. When relaxed, it presents the appearance of an in- 

 verted and irregularly shaped cup or basin, but w r hen in a 

 state of contraction it becomes nearly a plane surface. Hence 

 this muscle enlarges the chest by depressing its lower surface, 

 thereby forming a partial vacuum. 



248. Which muscles of the back are used in forced respiration ? Give the origin and 

 insertion of the two Serrate Muscles. Why called " Serrate V 249. Give the form of 

 the Diaphragm. What two cavities of the body does it separate? What is it an essen- 

 tial agent in effecting ? 



