THE OSSEOUS SYSTEM. 273 



general follows the contour of the medullary spaces and cells. The 

 flat and short bones present a similar arrangement internally, whilst the 

 cortical substance of these bones diifers from that of the cylindrical, 

 only in the circumstance, that the fundamental lamellae, in the flat bones, 

 form layers parallel with both surfaces of the bone. The thickness of 

 the fundamental lamellae in the cranial bones (parietal), is sometimes 

 the same in both aspects, and varies from 0'08 to 0-16 of a line, some- 

 times they are wanting in vascular situations, and in places, wholly so, 

 on the external aspect of the bone, in which case the Haversian lamellae 

 reach almost to the surface. 



With respect to the intimate structure of the osseous lamellae, which 

 is best studied in transverse sections, dried, polished, and sufficiently 

 thin, there is usually evident, besides the bone-cells and canaliculi, in 

 the generally not very distinct lamellae, an extremely fine though very 

 distinct punctuated appearance, so that the whole osseous tissue appears 

 granular, and to be composed as it were of separate, densely crowded, 

 pale granules, measuring 0-0002 of a line (Fig. 114). If water or 

 weak syrup, or albumen, be applied to a slice of bone, it assumes a 

 condition probably similar 

 to that which it possesses Flg 



during life. The lamellae, 

 for the most part (both in 

 transverse and perpen- 

 dicular sections), become 

 clearly visible, and their 

 granular aspect is quite dis- 

 tinct, although not so de- 

 fined as before the bone was 

 thus treated. For in the first place, together with the granules, there is 

 exhibited a close, pale striation, referable to the canaliculi, which are filled 

 with fluid and which, extending in various directions through the tissue, 

 renders its delineation more complex ; there are also apparent in each 

 lamella, as it were, two layers, one pale and more homogeneous, the 

 other darker and granular, which latter chiefly is striated. When this 

 condition is clearly displayed, an extremely delicate marking is produced, 

 resembling that seen in transverse sections of certain urinary calculi 

 (Fig. 113). When once seen in moistened sections, indications of this 

 arrangement will occasionally be observed in dried preparations. In 

 bone treated with hydrochloric acid, the granules and striae (dependent 

 on the canaliculi), in sections both transverse and perpendicular to the 



FIG. 114. Portion of a perpendicular section of a parietal bone, magnified 300 diame- 

 ters : a, lacunae, with pale, only partially-visible prolongations, filled with fluid as in the 

 natural state : b, granular matrix. The striated places indicate the boundaries of the 

 lamellae. 



18 



