305 



M. supra- aiui infiaspinaliis, between acromion and planum scapnlae. 

 It cannot be denied, iiowever. tliat in the mesencliyma, in wliicli 

 this bone develops, very jonng cartilage-cells are noticeable here 

 and there. These cells, however, have no intermediate matter as yet; 

 thev are little differentiated and it is difficnlt to distingnish them 

 from the mesenchyma-cells. So it is evident that besides bone-cells 

 also cartilage-cells develop in the mesencliyma. 



In an embryo of 90 mm. euchondrial as well as perichondrial 

 ossification takes place, the boundary between the two being no 



Acr 





Fig 7. Homo 90 mm. Margo 

 anterior scapulae transversal. 



PI. Sc. 

 Fig. 8. Homo 90 mm. Scapula trans- 

 versal Acr. = Processus acromialis 

 J.c. = Joint-cavity. PL Sc. = Planum 

 scapulae. 



longer perceivable. The peculiar character of the perichondrial ossi- 

 fication along the margo anterior is remarkable. In the place of 

 the formation of compact bone, which in other cases occnrs with 

 perichondrial ossification e.g. that of the long bones, we see here a 

 boiiy framework encircled by mesenchyma. Fig. 7 shows a cross 

 section through the margo anterior. 



The study of this object (embryo of 90 mm.) shows remarkable 

 peciilarities of the growth of the spina scapnlae. In the mesencliyma 

 between M. supra- and infraspinatus a distinct cartilage is now 

 recognizable. It is quite independent of the other mass of cartilage 



