OSSEOUS TISSUE. 323 



1. The Lacuna and Pores of Osseous Tissue. 



The lacuna (or bone-corpuscles) in man vary but little in size 

 and shape. Most of them are shaped like a melon-seed ; though 

 some are more fusiform, or even spherical. Their length averages 

 12*00 to s&o" f an i n k 5 some are > however, as short as s ^ o f an 

 inch, and some as long as ^J^ of an inch. They are 4 ^^ to y 

 or even j^u^ ^ an J nc h broad; and from gg 1 oc to 5 oV^ f an 

 thick or deep. Their three dimensions are usually as 6:2:1. The 

 spherical lacunae are from ooW to isVo of an inch in diameter. 

 They are placed so near together that 709 to 1120 (average 910) 

 occur within a surface of ^ of an inch square, (ffarting.) 



The pores, or canaliculi, average j^Viy to ?iu f an m h i n length, 

 the highest extreme being ^^ of an inch. They are T? &tfo to 

 F f an i nc h i n diameter at their origin from the lacuna?, and 

 o o to 40^0 at their finest extremities the average being about 

 s^irou- I n horizontal sections of the lacunas they appear as holes 

 T^THF to 57jV?r f an i nc ^ apart. In transverse sections they pro- 

 duce the radiating strias from being viewed in several planes, and 

 appear to be somewhat closer together or T5 o^ to T <jc>!)Ty of an 

 inch apart. The canaliculi ra- 

 diate from the lacunas in all di- ] 

 rections; and are branched and 

 irregular, and often curved, in 

 their course. A lacuna, there- 

 fore, together with its radiating 

 pores, forms an imperfect sphere, 

 gio to 3 IQ of an inch in diame- 

 ter. The pores of the different 

 lacunae anastomose freely with Portion of the gurface of the 



each Other, and tWO thus COn- seen on the external aspect. The numerous points 



nected sometimes measure , t> t^5^p^t^2?l 



to ^1^ of an inch in length. Pores belong, appearing from a greater depth. 

 , Magnified 360 diameters. (Ki'lliker.') 



They terminate m coecal extre- 

 mities only on limited spots; the most external, opening on the sur- 

 face of the bone (except when this is covered by cartilage or the 

 insertion of ligaments and tendons), as shown by Fig. 213. Thus 

 the entire structure of the bones is everywhere penetrated by a 

 connected system of cavities and pores, by which the nutritive fluid 

 from the vessels is carried to every part. 



