236 ANATOMY IN A NUTSHELL. 



hour more would be killed than are by this so-called solar plexus blow. The 

 diaphragm is the chief muscle of respiration. The lower ribs may fall down 

 thus drawing the diaphragm out of its natural position, in this way somewhat 

 obstructing the passing of the blood through the aorta. I have known of one 

 case in which the diaphragm was pulled down by the lower ribs causing an 

 irregular action of the heart. As soon as they were replaced the heart acted in 

 a natural manner. Tight lacing, or any cause whatsoever which will impair 

 the natural action of the diaphragm will cause much pain. Man is the only 

 animal in which the transverse diameter of the diaphragm is greater than the 

 antero-posterior. It begins to be developed about the ninth week of fetal life 

 and grows from the circumference to the central tendon. All mammals or 

 milk-giving animals have a diaphragm. Man and horse are examples of land 

 animals, the whale and the sea cow are examples of water animals which have 

 diaphragms. Birds possess a rudimentary form, which is best shown in the 

 abteryx. 



LESSON LXIV. 



The muscles which help the Diaphragm in tranquil inspiration are (1) 

 Intercostals, (2) Levatores costarum, and (3) The Scaleni. Those which help 

 it in forced inspiration are (1) Trapezius, (2) Pectoralis minor, (3) Pectoralis 

 major (?) (4) Serratus posticus superior, (5) Serratus posticus inferior, (6) 

 Rhomboideus major, (7) Rhomboideus minor, (8) Serratus magnus, (9) Sterno- 

 cleido-mastoid, (10) Ilio-costalis, (11) Quadratus lumborum. 



Tranquil expiration is caused by the elasticity of the lungs and that of the 

 chest walls. The muscles of forced expiration are (1) External oblique, (2) In- 

 ternal oblique, (3) Transversalis, (4) Rectus abdominis, (5) Internal inter- 

 costals, (6) Triangularis sterni. 



The sternum (Plates XCTI-XCIII.) is about six inches long and is situated 

 in the median line of the thorax in front. It is flat anteriorly and concave pos- 

 teriorly. It is broadest above and pointed below, and constricted at the junc- 

 tion of the manubrium with the gladiolus. The manubrium or first piece of the 

 sternum is narrow below, but broad above. The anterior surface of the manu- 

 brium is concave vertically but convex transversely. The Pectoralis major 

 and Sterno-cleido-mastoid are attached to the lateral aspect of this surface. 

 The upper border of this part forms the interclavicular notch, on each side of 

 which is an oval facet for the articulation of the clavicle. The lateral border 

 articulates above with the cartilage of the first rib and below with the upper 

 poit ion of the cartilage of the second rib. The low r er border articulates with 

 the gladiolus. The posterior surface is concave and gives attachment to the 

 Sterno-hyoid and Sterno-thyroid muscles. The gladiolus or second portion is 

 longer, narrower and thinner than the manubrium. It is broadest below. 

 The anterior surface gives attachment to the Pectoralis major. Three trans- 

 verse lines, indicating the original divisions of the gladiolus into four portions, 

 pass from the third, fourth, and fifth articular facets across the bone. These 

 lines are not so well marked on the posterior surface. This surface is concave 



