SVENSKA EXPEDITIONEN TILL MAGELLANSLÄNDERNA. BD. II. N:0 7. 157 



ness, witli regard to the exterior appearance of the dermal 

 ossicles of these animals, is tlms so great that there can 

 hardly be any characteristics of generic difference gotten 

 from the same. Ameghino does not mention if in his ossicles 

 of »Neomplodon» there are any depressions like those in the 

 Mylodon ossicles or not. For the study of the microscopical 

 structure I have prepared sections as well through the fossil, 

 as the recent ossicles. If we then first study the sections 

 through the ossicles of »Neomylodom, we shall tind them cotn- 

 posed of bony tissue, but of a very peculiar appearance. The 

 ossicles are compact and have no lamellated structure except 

 at the surface, where in some places, but not everywhere, a 

 few lamellre can be seen, but these are not very distinct, 

 and sometimes there is only a narrow translucent zone cor- 

 responding to one lamel which however can also be wanting. 

 This seems to indicate that the continued growth is eifected 

 by apposition of peripherical lamellre. The main mass of 

 the ossicle is composed of bony substance with the »bone- 

 corpuscles» scattered without any regularity or any System. 

 But the most characteristic feature is the abuudance of fibrils 

 of connective tissue. These iibrils, united into big bunches, 

 traverse the ossicles in every direction, and cross each other 

 linder diiferent angles and are woven or plaited together, so 

 there is hardly any space free from them (fig. 8). The only 

 system of arrangement that can be seen is that the fibrils 

 always run in bundles, not singly. The bloodvessels which 

 perforate the ossicles are situated in canals just wide enough 

 to give space to the vessels. These canals, however, are, as 

 a rule, not like the Haver's canals in common bone, sur- 

 rounded by concentrical lamella 1 , but they only just perforate 

 the tissue. The fibrils bend to the side when approaching 

 the canals for the bloodvessels, it therefore often seems on 

 sections, on which the vessels have been transversally cut, as 

 if they were surrounded by a tube of more translucent ma- 

 terial (a single lamel). Exceptionally, real concentrical la- 

 mellee are developed, just as in common bony tissue. I have, 

 for instance, on one section counted three well developed la- 

 melhe round a vessel, and at another place four such lamell«\ 

 but this is not a common occurrence. It shows, however, 

 that the structure of the dermal ossicles is not quite ab- 

 errant from common bony tissue. 



