DIMENSIONS AND EXPANSIBILITY OF THE THORAX. 



217 





respiration, the abdominal muscles stand foremost. They dimmish the 

 size of the abdominal cavity, and thus press the viscera upward against 

 the diaphragm. The triangular muscle of the sternum draws downward 

 the sternal extremities of the united cartilages and bones of the ribs 

 from the third to the sixth, which have been elevated during inspira- 

 tion. The posterior inferior serratus depresses the four lowest ribs, the 

 others necessarily following, being assisted by the quadratus lumborum, 

 which is capable of depressing the last rib. According to Henle, how- 

 ever, the posterior inferior serratus fixes the lower ribs so as to with- 

 stand the pull of the diaphragm, thus aiding inspiration. Landerer 

 even asserts that in the lower parts of the chest the movements of the 

 ribs enlarge the thoracic cavity downward. 



In the erect posture and with a fixed spinal column, deep inspiration and 

 expiration are accompanied by a displacement of the bodily equilibrium. During 

 inspiration the center of gravity is moved slightly forward by the protrusion of the 

 chest and the abdominal walls. In deep inspiration the straightening of the 

 spinal column and the consequent throwing back of the head act as a compensation 

 for the projection of the anterior trunk- wall. 



DIMENSIONS AND EXPANSIBILITY OF THE THORAX. 



It is of considerable importance for the physician to know the dimensions of 

 the thorax, as well as the extent of its expansion in various directions. With 

 inspiration the thorax is enlarged in all its diameters. The diameters of the thorax 

 are determined by means of calipers; the circumference is measured by means of 

 the centimeter tape-measure. 



In well-built men the upper circumference of the chest, close under 

 the arms, measures 88 cm.; in women it is 82 cm. The lower circum- 

 ference, at the level of the en- 

 siform cartilage, is 82 cm. in 

 men and 78 cm. in women. 

 When the arms are held hori- 

 zontally the measurement taken 

 during expiration just below 

 the nipples and the angles of 

 the scapulae equals half the 

 body-length, that is, 82 cm. in 

 men; during deepest inspira- 

 tion it is 89 cm. At the level 

 of the ensiform cartilage the 

 circumference is about 6 cm. 

 less. In old persons the upper 

 circumference is diminished, 

 being smaller than the lower 

 measurement. Usually the right 

 half of the thorax is some- 

 what larger than the left, on account of the greater muscular 

 velopment. The longitudinal diameter of the thorax, from the clavicle 

 to the lowest edge of the ribs, varies considerably. 



The transverse diameter (distance between the lateral surfaces, 

 in men, from 25 to 26 cm., above and below; in women, from 23 to 24 

 cm. Above the nipples it is about i cm. greater. The antero-posteno 

 diameter (measured from the anterior surface of the sternum t 

 of a spinous process) is 17 cm. in the upper part of the thorax, and 19 cm. 



FIG. 82. Cyrtometer-curve from a Case of Left-sided 

 Retraction of the Thorax in a Twelve-year-old Girl 

 (after Eichhorst). 



