FIBROUS TISSUES. BONE. 693 



completeness to the doctrine which has been thus sketched, it may be 

 stated with considerable confidence that the tendency of all recent 

 inquiry has been to show, that the bodies of even the highest 

 Animals are everywhere penetrated by that Sarcodic substance of 

 which those of the lowest and simplest are entirely composed ; and 

 that this substance, which forms a continuous network through 

 almost every portion of the fabric, is the instrument of the Forma- 

 tion and Nutrition of the more specialized Tissues. 



541. As it is the pm*pose of this work, not to instruct the Pro- 

 fessional Student in Histology (or the Science of the Tissues), * but 

 to supply Scientific information of general interest to the ordinary 

 Microscopist, no attempt will here be made to do more than de- 

 scribe the most important of those distinctive characters, which the 

 principal Tissues present when subjected to Microscopic examina- 

 tion; and as it is of no essential consequence what order is adopted, 

 we may conveniently begin with the structure of the Skeleton, f 

 which gives support and protection to the softer parts of the 

 fabric. 



542. Bone. — The Microscopic characters of Osseous tissue may 

 sometimes be seen in a very thin natural plate of Bone, such as in 

 that forming the Scapula (shoulder-blade) of a Mouse ; but they 

 are displayed more perfectly by artificial Sections, the details of 

 the arrangement being dependent upon the nature of the specimen 

 selected, and the direction in which the section is made. Thus 

 when the shaft of a ' long ' Bone of a Bird or Mammal is cut-across 

 in the middle of its length, we find it to consist of a hollow cylinder 

 of dense bone, surrounding a cavity which is occupied by an oily 

 marrow ; but if the section be made nearer its extremity, we find 

 the outside wall gradually becoming thinner, whilst the interior, 

 instead of forming one large cavity, is divided into a vast number 

 of small chambers or cancelli, which communicate with each other 

 and with the cavity of the shaft, and are filled, like it, with mar- 

 row. In the Bones of Reptiles and Fishes, on the other hand, 

 this ' cancellated ' structure usually extends throughout the shaft, 

 which is not so completely differentiated into solid Bone and 

 Medullary cavity as it is in the higher Vertebrata. In the most 

 developed kinds of ' flat ' Bones, again, such as those of the head, 

 we find the two surfaces to be composed of dense plates of bone, 

 with a ' cancellated ' structure between them ; whilst in the less 



* For more detailed information, the student may be specially referred 

 to Messrs. Todd and Bowman's "Physiological Anatomy," Dr. Sharpey's 

 Introduction to "Quain's Anatomy," (4th Edit., 1867), Prof. Kolliker's 

 "Manual of Human Histology," Prof. Virchow's "Cellular Pathology," 

 translated by Dr. Chance, and an important Review of the Cell-Theory, 

 by Prof. Huxley, in the " Brit, and For. Med.-Chir. Review," Vol. xii. 

 (Oct. 1853), p. 285. 



t This term is used in its most general sense, as including not only the 

 proper Vertebral or internal skeleton, but also the hard parts protecting 

 the exterior of the body, which form the Dermal skeleton. 



