32 THE sternum: its early development and ossification. 



DESCRIPTION OF PLATES II., III. 



Fig. 1. Human embryo (sagittal section). 



Fig. 2. Rat 9 mm. Section across bottom of praecervical sinus. 



Fig. 3. ,, ,, Sagittal section through chest wall. 



Fig. 4. J, ,, Transverse section through middle of chest 



wall, showing ossifying ribs and absence 



of sternum. 



^^' ' ' \ Magnified seven times, showing clavicles, 



„!^" y' " " \- pre-sternum, meso-sternum, and costal 

 £,}§• I- " " I cartilages. 



Fi« 9 Rat 10 mm ( ^^8^^^^*^^ twenty-eight times, to show char- 



-p,.°' „■ '-^ acteristic features of pre-sternum and 



»■ * " " ( meso-sternum. 



Fig. 11. Rat 10 mm. f Higher magnification, to show differentiation 



Fig. 12. ,, „ ) of tissue in sternum and costal cartilages. 



-p,.^' T / "I Magnified seven times, to show structure and 



T^.^' _■ " ■' ( connections of sternal elements. 

 Fig. 15. „ „ I 



1^ Magnified twenty-eight times, to show general 



Fig. 16. Rat 13 mm. < structure of sternum and connections of 



( costal cartilages. 



Fig. 17. Human sternum, 3rd month, 8 mm. long, magnified twenty- 

 eight times. 



Fig. 18. Human sternum, 3rd month, 10 mm. long, magnified twenty- 

 one times. 



Fig. 19. A-I. Sections of human sternum, 3rd month, 9 mm. long, 

 possessing sternal foramen and 8 costal cartilages, — magnified 18 times. 

 J. Reconstruction of same. 



Fig. 20. Rat embryo. Coronal section of cartilaginous sternum, 

 showing primary areolae, — magnified seven times.- 



Fig. 21. Coronal section of older rat's sternum, showing primary 

 areolae and absence of ossification in last piece of meso-sternum, — 

 magnified seven times. 



Fig. 22. Coronal section of older rat's sternum, showing primary 

 areolae, thickened perichondrium, and absence of bone formation be- 

 tween 6th and 7th costal cartilages. 



Fig. 23. Coronal section of sternum of mouse a few days after birth, 

 showing bone formation and cartilages. 



Fig. 24. Sternum (lower end) of rat 9 days old, showing ossifica- 

 tion. 



