60 OSSEOUS TISSUE. [sect. 27. 



il 

 in the orbit j around the kidneys ; in the mesentery and 



omenta ; around the spinal cord ; on nerves and vessels ; and in 



muscles. 



m. Ordinary areolar connective tissue, which is sometimes quite 

 poor in elastic fibres and plasm-cells, and sometimes abounds in 

 them, is found most extensively between the organs seated in the 

 neck, the thoracic, abdominal, and pelvic cavities; along the 

 course of all vessels and nerves; and in the interior of muscles, 

 nerves, and glands. 



In certain places, as in the vertebral canal and medulla of car- 

 tilage, it is of a gelatinous nature, like embryonal loose connective 

 tissue, and then contains in its meshes a fluid sometimes like 

 serum, sometimes containing mucus and albumen. 



Literature. — Zelinsky, Dc Telis Collam Edentibus. Dorp. 1852. Diss. Also 

 the treatises cited in § 224.. 



§ 27. Osseous Tissue. — Structurally, osseous tissue essentially 

 consists of a matrix, and of numerous microscopic cavities cvoo6'" 

 to 0'0i4'" in length, 0'003'" to O'ooj'" in breadth, and 0"002'" 

 to 0-004'" m thickness, disseminated in it, — the lacunae (bone cor- 

 puscles of authors). The former, which is of a white colour, is 

 sometimes more homogeneous, sometimes finely granular, very 

 frequently lamellated, and, from its intimate union with calcareous 

 salts, hard and brittle. 



The lacunae are generally lenticular in shape, and are, in most 

 cases, connected to each other by numerous fine processes, the 

 canaliculi, by which some of them also open upon .the outer sur- 

 face of the bones, and others into the larger and smaller medullary 

 spaces in the interior. The lacuna? and canaliculi contain a pel- 

 lucid matter, which may be designated as the nutrient fluid of the 

 bones ; and, in many cases, a cell-nucleus also appears to be en- 

 closed in the lacunae, and may, perhaps, be present in all. Besides 

 these two most important elements, which are never absent in the 

 bones of the higher animals, most of the bones contain numerous 

 vessels and nerves, and frequently, also, a special substance sup- 

 porting these, the medulla. This consists either of ordinary 

 adipose tissue, or of a loose, scanty areolar tissue, with but few fat- 

 cells and numerous proper marrow-cells, as they are called. These 

 soft parts fill up the large central cavities of the bones, and those 

 of the spongy substance; they also, at least in part, occupy the 

 narrow canals traversing the compact substance, the vascular or 



