344 The Development of the Connective Tissues 



its fibrils. Finally, when the cartilage is complete, the fibrils of the 

 exoplasm are entirely obscured by the ground substance. 



Sections stained by Mallory's method show that the endoplasm is 

 almost wanting around the nuclei of the syncytium immediately below 

 the ectoderm. Practically none is seen until the nuclei shift into the 

 spaces between the exoplasm in the neighborhood of the cartilage. In 

 this region the nuclei are larger than those more distant and in the 

 region of the completed cartilage both nuclei and endoplasm are several 

 times as large as in the surrounding syncytium. When the cartilage 

 is fully developed the relatively large granular nuclei are encircled with 

 vacuolated endoplasm. Each nucleus and endoplasm is encircled by a 

 transparent space separating it from the surrounding exoplasm or 

 ground substance. In specimens which have been macerated in Miil- 

 ler's fluid for a day, then washed and hardened in alcohol, and stained 

 with hsematoxylin and congo red, it is seen that no space exists between 

 the endoplasm about the nucleus and the ground substance. By this 

 method the endoplasm becomes more marked and the ground substance 

 less marked than in the specimens hardened in Zenker's fluid and 

 stained by Mallory's method. 



Specimens of developing cartilage macerated as described above show 

 at the jimcture of the cartilage v;-ith the connective-tissue syncytium 

 a zone of ground substance which will noL stain with hgematoxylin, but 

 tinges with congo red (Fig. 9). Passing from the surrounding syncy- 

 tium into the developing cartilage, the nuclei become larger, the exo- 

 plasm increases, condenses and obscures the endoplasm. Gradually the 

 fibrillated exoplasm becomes granular, making it appear as if the nuclei 

 were imbedded in a continuous granular mass. This all seems to be due 

 to the maceration in Mliller's fluid. On the periphery of the cartilage 

 there is a zone of ground substance which does not stain with hema- 

 toxylin but tinges with congo red (Fig. 9). This zone is of the width of 

 one or two nuclei which are surrounded with some endoplasm. The 

 completed ground substance, which stains with hgematoxylin, begins 

 quite abruptly; the nuclei are encircled with a considerable quantity of 

 endoplasm, filling almost entirely the spaces in Avhich they lie. 



The definite conclusion to be drawn from the above specimens is that 

 the ground substance of the cartilage is deposited directly into the 

 exoplasm of the syncytium and its nuclei and endoplasm become the 

 cartilage cells. 



Not only can the direct connection between the ground substance and 

 the exoplasm be seen in the occipital cartilage, but also at the dorsal 

 side of the bodies of the vertebrjB, the petrous portion of the temporal 



