44 ANATOMY AND PHYSIOLOGY 



the base of the coccyx. Since the spinal canal contains the spinal 

 cord there must be places of exit for the spinal nerves; these are 

 found in the intervertebral foramina between the roots of the 

 arches. 



The spine has four curves: cervical, thoracic, lumbar, and sacral. 

 These are normal curves. 



The cervical and lumbar curves are concave posteriorly, as is 

 seen to a slight degree in the back of the neck, and more plainly 

 in the so-called " small of the back"; while the thoracic and sacral 

 curves are concave anteriorly, to accommodate the organs in the 

 thorax and pelvis. 



These curves are caused by variations in the thickness of the bodies and 

 cartilage discs. So-called "spinal curvature" is an excessive or abnormal 

 curve. If anterior it is lordosis; if lateral, scoliosis; if posterior, kyphosis. 



A lateral curve usually exists in the upper thoracic region, but 

 this may be called accidental, as it is explained by the excessive 

 use of one or the other arm. 



THE TRUNK 



INCLUDES THE THORAX, ABDOMEN AND PELVIS 

 BONES OF THE THORAX 



Sternum i 



Ribs (costae) 24 



Thoracic vertebrae 12 



Sternum or breast-bone. Placed in the front of the thorax. 

 It is about 6 inches long, flat in shape and structure, and its two 

 surfaces are called anterior and posterior. It has three divisions, 

 the manubrium, the body, and the xiphoid appendix (Fig. 40). 



The upper border of the sternum is notched the sternal (or 

 jugular) notch; the lateral borders give attachment from above 

 downward to the clavicle and the cartilages of the first seven ribs. 

 The xiphoid appendix is the lowest portion of the bone and gives 

 attachment to some of the muscles of the abdomen. It remains 

 cartilaginous until middle life. 



Ribs (costtz). Twelve in each side of the thorax, forming a 

 series of movable elastic arches. They consist of a bony portion 

 (the costal bone) and a flexible portion (the costal cartilage) . They 

 are flat in structure, curved in shape. 



