546 



MOVEMENTS. 



lacuna. They send out prolongations into the canaliculi, but it has been impossible to 



ascertain positively whether or not they form membranes lining the canaliculi through- 

 out their entire length. 



Marrow of the Bones. I\\Q peculiar 

 structure called marrow is found in the me- 

 dullary cavities of the long bones, filling 

 them completely and moulded to all the 

 irregularities of their surface. It is also 

 found filling the cells of the spongy portion. 

 In other words, with the exception of the 

 vascular canals, lacunse, and canaliculi, the 

 marrow fills all the spaces in the fundament- 

 al substance. We know very little of the 

 functions of the marrow, and we shall there- 

 fore pass it over with a brief description. 



It is now settled that the cavities of the 

 bones are not lined with a membrane corre- 

 sponding to the periosteum, and that the 

 marrow is applied directly to the bony sub- 

 stance. In the foetus and in very young 

 children, the marrow is red and very vascu- 

 lar. In the adult it is yellow in some bones 

 and gray or gelatiniform in others. It con- 

 tains certain peculiar cells and nuclei, with 



amorphous matter, adipose vesicles, connective tissue, blood-vessels, and nerves. 



Medullocells. Robin has described little bodies, existing both in the form of cells 



and free nuclei, called medullocells. These are found in greater or less number in the 



FIG. 165. Transverse section of bone, from the shaft 

 of the human humerus ; magnified 180 diameters. 

 (From a photograph taken at the United States Army 

 Medical Museum.) 



This figure is introduced for the reason that it is a copy 

 of a photograph of the actual structure. 



FIG. ~L66.one-corp'iwcles, with their prolongations. (Rollett.) 



bones at all ages, but they are more abundant in proportion as the amorphous matter and 

 fat-cells are deficient. The nuclei are spherical, with borders sometimes irregular, gen- 

 erally without nucleoli, finely granular, and from ^ to ^Vo of an inch in diameter. 



