THE THORAX. 171 



tongue through to the posterior surface of the hyoid bone and thence downward and 

 forward to the isthmus of the thyroid gland. It begins to atrophy in the fifth week 

 and is obliterated by the eighth. According to Sutton these cysts are never congen- 

 ital but occur soon after birth or as late as the fourteenth year. They appear as 

 rounded, cystic tumors just below the hyoid bone or over the thyroid cartilage. They 

 either inflame and break of their own accord, discharging externally, or are opened by 

 the surgeon and, contrary to what is the case in hydroceles of the neck, never tend to 

 disappear, but a sinus remains. At times it almost heals, then the contents accumulate 

 and a cyst forms, this again breaks and a sinus results as before. In attempting a cure 

 by operation the sinus should be followed up behind the hyoid bone. In one case after 

 two failures of attempted excision a cure was obtained by destroying the tract by 

 introducing a small galvanocautery point. Unless every portion of the lining mem- 

 brane be completely destroyed the cells will go on secreting and reproduce, in a 

 short time, the original condition. Failure to cure these sinuses and cysts by excision 

 often occurs, notwithstanding the exercise of the greatest care. 



The lower portion of the thyroglossal duct may persist in the form of the pyramid 

 cr third lobe of the thyroid gland, which arises from the isthmus or from the left side 

 and ascends as far as the hyoid bone, to which it is attached. 



THE THORAX. 



The thorax or chest is that portion of the trunk which lies between the neck 

 and the abdomen. It is composed of a bony framework reinforced by soft parts, 

 and contains the main organs of circulation and respiration. The oesophagus, an 

 organ of the digestive tract, simply passes through it to the regions below. The 

 chest-walls as well as the parts contained within them are affected by wounds and 

 disease, especially the heart and its associated great vessels, and the lungs and 

 pleurae. These organs are essential to life, like the brain and spinal cord, and like 

 them, are encased in a bony framework. It is an example of bones performing a 

 protecting function in addition to a supporting one. 



The functions of the heart and lungs are influenced by constitutional diseases in 

 addition to their own local affections, hence they serve as guides to the general bodily 

 condition, and the condition of the respiration and circulation is continually being exam- 

 ined for the purposes of diagnosis, prognosis, and treatment, even when the heart and 

 lungs themselves are not involved. To make these examinations intelligently, neces- 

 sitates a knowledge of the organs themselves and their relation to one another and the 

 surrounding parts. This is essential for the physician even more than the surgeon. 



The chest-walls are composed of a bony framework joined and bound together 

 and covered by soft parts. 



The bones of the chest consist of the sternum, ribs, and thoracic vertebra. The 

 clavicle and scapula compose the shoulder-girdle and belong to the upper extremity. 

 The human skeleton is divided into an axial portion and an appendicular portion. The 

 axial portion embraces the skull, the vertebral column, including the sacrum and 

 coccyx, the hyoid bone, the sternum, and the ribs. The appendicular portion con- 

 sists of the shoulder-girdles and upper extremities and the pelvic girdles and lower 

 extremities. 



The bony chest is subject to disease and injury as well as to defects in develop- 

 ment, and to deformities due to these causes. 



Shape of the Chest. The chest is conical in shape, being small above and 

 large below. In transverse section it is kidney-shaped, the hilus of the kidney being 

 represented by the vertebrae. In the foetus the anteroposterior diameter is greater 

 than the transverse, thus resembling the thorax in the lower animals. After birth 

 and in infancy the two diameters are nearly equal, hence we have the rounded chest 

 of the child. As growth and development progress the transverse diameter increases 

 more than the anteroposterior, so that at about the second year the chest has become 

 oval and in adults the transverse diameter is one-fourth greater than is the antero- 

 posterior. 



Variations in the shape of the chest are mainly the result of disease. In child- 

 hood, rachitic disease (rickets) produces a lateral flattening and a projection of the 



