234 CONNECTIVE TISSUE. 



lated layer beneath the periosteum, as well as at the border of 

 the central marrow-tube. Where these layers are pierced by 

 vertical vascular canals, such canals, as a rule, are surrounded 

 by more or less perfect sheaths of lamellae. 



From these observations it follows that, independently of the 

 general growth of the bone, the living matter stored up in 

 the medullary spaces is the forming material of bone. The ele- 

 ments termed " medullary cells/' as well as " osteoblasts," are 

 transformed into bone-tissue, and in this way the lamellated 

 layers of the bone become broader, and the medullary spaces, 011 

 the contrary, narrower. The systems produced by the contents 

 of a medullary space surround smaller systems, the formation 

 of which depends upon the single blood-vessels of the former 

 medullary space, which now occupy the centers of the vascular 

 canals. 



All systems of lamellae, therefore, are vascular territories, as 

 it were, stratified pillars, the main longitudinal direction of 

 which agrees with the course of the blood-vessels in their centers. 

 From the main longitudinal course of this structure, branch sys- 

 tems, frequently in the oblique, rarely in the transverse, direction. 

 The formation of non-lamellated intermediate bone-tissue also 

 depends upon the blood-vessels. 



Watching the contents of the vascular canals with high ampli- 

 fications, I observed the following features : 



In the bone of a dog about six months old, each vascular 

 canal contains one or two blood-vessels, of varying caliber and 

 of a straight course. I have several times seen nerves running 

 along with the vessels, though my method of preparation was 

 not favorable to the clearing up of nerve-tissue. The wall of the 

 blood-vessel, as a rule, exhibits the simple structure of a capillary, 

 with occasional spindle-shaped thickenings. The vessel is sur- 

 rounded by a light rim, traversed by delicate grayish spokes, 

 connecting the wall of the vessel with the neighboring spindle- 

 shaped elements. The latter ensheath the perivascular space, 

 either in a single flat layer or in several strata, and are also inter- 

 connected by short projections. Between the spindles and the 

 bone- wall there is again a light rim, traversed by delicate off- 

 shoots, which directly connect the spindles with the offshoots of 

 the bone-corpuscles. 



In the tibia of a dog over a year old, I found similar vascular 

 canals ; besides numerous canals which, sometimes in places and 

 sometimes in their whole length, contained only a capillary 



