96 MANUAL OF HISTOLOGY. 



looser texture. The external portion may be composed of sin- 

 gle, double, or treble laminae of varying thickness. The inner 

 or osteogenetic portion is of great interest and importance, 

 as it contains the osteoblasts, which are active agents in the 

 formation of a great part of all bones, as we shall presently 

 see. 



Development of bone. Views as to the method by which bone 

 is formed have undergone great changes within the past few 

 years, and it may be stated that most modern observers have 

 given in their adhesion to the theory that bone is not developed 

 by a calcification of cartilage, but by a long and complicated 

 series of changes inaugurated by the corpuscles of the marrow 

 cavities, on the one hand, and those of the periosteum, on the 

 other. These conclusions have been the result of very extended 

 researches conducted by a variety of methods and upon many 

 kinds of animals. 



As the mode of growth in man and horned cattle is identical, 

 a good method of procedure is as follows. Take the hoof of a 

 yearling bullock, and, removing the bones, macerate them a 

 few days in a 10 per cent, watery solution of h3 7 drochloric acid 

 and then in chromic acid (gr. ij. lj.). In a few days they 

 will be decalcified sufficiently to allow of a thin section being 

 shaved off from the surface so as to include parts where ossifi- 

 cation has already commenced. The sections may then be 

 stained in a neutral solution of carmine and mounted. The 

 gradual stages between the advancing bone and the liquefying 

 cartilage can now be studied. Following the changes from the 

 surface of the articulation toward the centre of the bone, there 

 is seen at first, beneath the fibrous layer, a stratum of hyaline 

 cartilage. The corpuscles are long, flattened, and lie parallel 

 with the surface. Passing to a greater depth they become 

 larger, and increase in number by gradual progression. As 

 these capsules enlarge and their contents multiply, they 

 begin to be arranged about the wall of the cavity, while 

 the matrix gradually wastes away. A little farther and 

 there is a deposit of calcific material in the intercapsular sub- 

 stance. Another step internally and the cartilage capsules 

 have in part coalesced, and now they are beginning to be filled 

 by the marrow tissue pushing up from the central parts of the 

 bone. When the connective tissues and vessels that constitute 

 this arborescent growth have entered the capsules, the corpus- 



