THE OSSEOUS TISSUE. 169 



cavities contain granular matter, and have the calcigerous 

 tubes running into or passing from them in a stellate form. 

 There are also certain lines or stride described by Deutsch, 

 but which Wilson, in his observations, makes identical 

 with the calcigerous tubuli. 



The bones have 



FIG. 32. 



two membranes, the 

 one covering their 

 outer surface, called 

 the periosteum, the 

 other lining the in- 

 terior of their cavi- 

 ty, called the me- 

 dullary membrane. 

 The periosteum is a 

 fibrous membrane, 

 and has been described under the head of the fibrous sys- 

 tem. It covers every part of the bone except the articular 

 surface ; it is continuous, at the extremities, with the liga- 

 ments, loosely attached in infancy, but closely adherent in 

 adult bone. 



The periosteum is very vascular, and both its fibres and 

 vessels pass together into the bone. 



The medullary membrane is an exceedingly delicate mem- 

 brane, composed of a very fine, soft, cellular tissue, con- 

 taining numerous minute blood vessels. It can be traced 

 lining the whole interior of the medullary cavity, and ex- 

 tending into the medullary cells, and,, it is believed, into all 

 spongy structure wherever found. This membrane forms 

 vesicles for containing the marrow, which fills the reticular 

 spaces in bone. In birds these are occupied by air. Both 

 it and the periosteum accompany the blood vessels through 

 bone. Besides secreting the marrow, this membrane serves 

 to nourish the bones. 



The blood vessels supplying bones are numerous. The 

 arteries are referred to three classes. 1st. Those which 



FIG. 32 represents a transverse section of bone with the Haversian canals 

 and lacunae. 



