164 



HUMAN ANATOMY. 



The top of the sternum is on a level with the disk between the second and third 

 thoracic vertebrae ; the junction of manubrium and body of sternum is on a level 



Fig. 189. 



V 



\ 



'0 



SD 





^\ 



Q' 



a 



Transverse section through thorax at level of 

 third thoracic vertebra. (Btaiine.) 



Transverse section at level of fourth thoracic 

 vertebra. {Braune.) 



^ 



with the top of the fifth thoracic vertebra. Less accurate, but still useful, is a third 

 level : the lower end of the body of the sternum is opposite the ninth thoracic 



vertebra. Accompanying diagrams, 



f^"^- 190- taken from Braune, show the varia- 



^ GHZ) • tions of size, form, and relations at 



different levels (Figs. 188 to 191). 



The breadth of the intercostal 



spaces is very different in diverse 



parts. Between the tubercles and 



angles it is pretty nearly the same 



Q 5 throughout, butthe lasttwo spaces are 



a little broader. The first two spaces 



are much the broader at the sides 



and in front. They are broad near 



the sternum as far down as the fifth 



cartilage. At the sides the ribs are 



very close together, from the fourth 



to the ninth often almost in contact. 



The lowest spaces are again broader. 



The Thorax in Infancy and Childhood. — At birth the thorax is relatively 



insignificant. The sternum is small and undeveloped in the lower part. The ribs 



are more horizontal. The top of 



'0 



Transverse section at level of eighth thoracic vertebra. 

 (Braune.) 



Fig. 191. 



^ 



7 



'0 



^' 



the sternum is opposite the body 



of the first thoracic vertebra. In 



the course of the first year it lies 



opposite the upper part of the 



second, and at five or six has 



reached its definite level opposite 



the disk between the second and 



third thoracic vertebrae. The lower 



part of the sternum is undeveloped, 



and the ribs do not fall so low at 



the sides. The want of breadth is 



very striking, while in the adult, 



throughout the chest below the 



level of the second costal cartilage, 



the antero-posterior diameter is to 



the transverse as i to 2^, or as 



I to 3 ; at birth it is as 2 to 3. 



We have found it at probably 



three years as i to 2 ; at five or six the thorax has nearly reached its permanent 



shape. 



Differences due to Sex. — The whole structure is lighter in women, but the 



'0 



i\ 



^ 



II 



I' 



f 



10 



Transverse section at level of eleventh vertebra. Shaded areas 

 (6, 7) are sections of costal cartilages. (Braune.) 



