EXPLANATION OF FIGURES 



PLATE I 



Fig. I. Human embryo (sagittal section). 



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



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



Fig. 4. „ ,, Transverse section through middle of chest wall, showing ossifying 



ribs and absence of sternum. 



Fig. 5. Rat 10 mm. 1 



^ 'S- "■ " " ( Magnified seven times, showing clavicles, presternum, mesosternum, 



Fig. 7. „ „ 1 and costal cartilages. 



Fig. 8. „ „ ) 



rig. 9. Kat 10 mm. 1 Magnified twenty-eight times, to show characteristic features of 

 Fig. 10. „ „ ; presternum and mesosternum. 



Fig. II. Rat 10 mm. Higher magnification, to show differentiation of tissue in sternum 

 and costal cartilages. 



PLATE II 



Fig. 12. Rat 10 mm. Higher magnification, to show differentiation of tissue in sternum 

 and costal cartilages. 



Fig. 13. Rat 13 mm. -1 



Tj- . , ( Magnified seven times, to show structure and connexions of sternal 



^'^- '+• " " f elements. 



Fig. 15. „ V ■' 



FV 16 Rat i^ mm i Magnified twenty-eight times, to show general structure of sternum 

 °' ' ' ( and connexions of costal cartilages. 



Fig. 17. Human sternum, third month. 8 mm. long, magnified twenty-eight times. 

 Fig. 18. „ „ 10 >, „ twenty-one „ 



Yie, 10. „ „ 9 „ possessing sternal foramen, and eight 



costal cartilages — magnified eighteen times. 



PLATE III 



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 mesosternum — magnified seven times. 



Fig. 22. Coronal section of older rat's sternum, showing primary areolae, thickened peri- 

 chondrium, and absence of bone formation between sixth and seventh costal 

 cartilages. 



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

 and cartilages. 



