THE PLEURA. 



1863 



of Wrisberg (cuneiform) and of Santorini (cornicula laryngis) are formed from 

 small portions separated from the epiglottis and the arytenoids respectively. The 



Neural canal 

 Spinal cord 

 Spinal ganglion 



v 



FIG. 1588. 



Vertebra 



Cardinal vei 





Right lung 



Right bronchus 



Diaphragm 



-Cardinal vein 



Aorta 



CEsophagus 



u 



r~Pleural cavity 



Inferior vena cava 

 Portion of transverse section of rabbit embryo, showing developing lungs. X 30. 



FIG. 1589. 



epiglottis and the cricoid possibly represent rudiments of the cartilages of the sixth 



and seventh branchial arches. 



Changes in the Relations of 

 the Lungs and Pleurae to the 

 Chest- Walls. At birth the thorax 

 is small, relatively very narrow, with 

 the lower part undeveloped and with 

 more horizontal ribs. The costal car- 

 tilages are relatively long to the ribs 

 proper. Nevertheless, at birth and in 

 childhood the borders of the lungs have 

 very nearly the same relations to the 

 chest-walls that they have in the adult, 

 excepting in front. Here they do 

 not extend so far forward, and conse- 

 quently the pericardium is at first less 

 covered by the left lung. The course 

 of the pleurae is much less certain. 

 Tanja found much variation in that of 

 the lower borders of the pleurae, the 

 latter crossing all the costal cartilages 

 fourteen times in twenty-four bodies 

 of children under two years and not 

 a single time in the adult. In eleven 



Section of foetal lune, showing compact character of unin- r ,1 ,1. i i-j 



flated pulmonary tissue! x 200. 01 the same series the pleurae did not 



meet behind the sternum, and in nine 



the left pleura did not reach it. He found neither of these conditions even once 

 in the adult. According to Mehnert, there is a very slight progressive sinking of 



