EXPLANATION OF PLATES 



The figures of these plates were made with a Leitz ^s homogeneous immersion 

 objective and a no. 1 Leitz ocular, at an original magnification of 785 diameters. 

 With the exception of figures 8 and 11, which are from human embryos, the 

 illustrations represent stages from the jaws of pig embryos. 



ABBREVIATIONS 



b.c, bone cell obi., osteoblast 



cap., capiHary ocl., osteoclast 



c.t., connective tissue str., striate edge of osteoclast 



mix., matrix of bone *, junction of confluent osteoblasts and 



osteoclast 



PLATE 1 



EXPLANATION OF FIGURES 



The preparations, from which the illustrations of this plate were made, are 

 from pig embryos, fixed in Zenker and stained with hematoxylin and eosin. 

 The reduced magnification is now 590 diameters. 



1 The basophilic syncytium, ocl., illustrates the first stage in osteoclast devel- 

 opment by the fusion of osteoblasts. 



2 The immature osteoclast, ocl., exhibits a transitional stage in stainability 

 between the basophilic osteoblasts, obi., and a typical oxyphilic osteoclast like 

 figure 4. 



3 An asterisk, *, marks the continuity between an osteoclast at the left and 

 the osteoblastic syncytium on the right. 



4 At the right is a bold osteoblast-osteoclast junction. On the left a 

 process from an osteoclast, in contact with the capsule of the bone cell, b.c, 

 illustrates an early stage of phagocytosis. 



5 Two later stages in the ingestion of bone cells by an osteoclast; the engulf- 

 ment of, b.c.', is farther advanced than of, b.c. 



6 Advanced osteoclastic degeneration. The nuclei are pyknotic, the cyto- 

 plasm highly vacuolated and palely staining. 



7 An osteoclast within a blood capillary. Such usually show evidence of 

 degeneration and suggest a method of filial removal. 



338 



