290 SPECIAL HISTOLOGY. 



quantity of osseous tissue, which is disposed in the form of 

 fibres, laminae, and small rods. When the spaces are of a 

 larger size, the substance is termed subst. cellularis, and when 

 smaller, subst. reticularis. The latter, in some situations where 

 the cavities are smaller, and the osseous partitions stronger, 

 approaches in character the compact substance, although it 

 does not actually become such ; and in others it passes without 

 any defined limit, into compact tissue. This does not, how- 

 ever, prove that the two substances are identical, but, as we 

 learn from observation of their development, depends simply 

 upon the circumstance that the spongy substance very fre- 

 quently arises in a partial expansion of the compact. The 

 share taken by the two substances in the formation of the 

 different bones, and parts of bones, varies very considerably. 

 It is only in a few situations that the compact substance is 

 met with by itself without vascular canals — as in the lamina 

 papyracea of the ethmoid bone, some portions of the lachry- 

 mal and palate bones, &c. It occurs more frequently, how- 

 ever, with vascular canals, and without spongy substance, as in 

 many individuals in the thinnest portion of the scapula, ilium, 

 acetabulum, cranial bones (ala magna, parva of the sphenoid, 

 the orbital process of the frontal bone, &c). Spongy sub- 

 stance with a thin compact cortex, without vascular canals, 

 exists in the auditory bones, on the surfaces covered with 

 cartilage of all bones, probably also in the smaller spongy 

 bones. In all other cases, and consequently in most situations, 

 the two substances are conjoined, but in such a way, that 

 sometimes the spongy substance predominates (spongy bones 

 and parts of bones), as in the vertebra, carpal and tarsal bones ; 

 sometimes the compact, as in the diaphyses of the long bones ; 

 or the two are in equal proportions, as in the flat bones. 



§ 89. 



Intimate structure of the osseous Tissue. — The osseous tissue 

 consists of a dense, for the most part indistinctly lamellar 

 fundamental substance or matrix, penetrated by vascular canals 

 and numerous minute microscopic spaces — the bone-cells, or 

 lacuna (bone-corpuscles of authors), having very minute hollow 

 processes, the bone-canaliculi. 



The vascular canals of the bones, or the Haversian canals 



