OSSEOUS TISSUE. 33 



T. S. OF DENSE FCETAL BONE (DECALCIFIED). 



EXAMINATION (L). The bone-matrix is yellowish and the corpuscles in the lacunae red. 

 Observe the ring of bone, not so dense as in the adult ; the Haversian canals are relatively 

 larger, and contain a layer of osteoblasts, which line them, and also a blood-vessel. The 

 outer layer of the periosteum is red and the deeper layer is yellowish, and between it and the 

 bone a layer of nucleated, somewhat cubical cells the osteoblasts which may be traced into 

 Haversian canals opening on the surface of the bone. (H). Observe the osteoblasts lying 

 on the bone, and here and there they may be traced into Haversian canals which run 

 horizontally and communicate with the surface of the bone. The bone-corpuscles are relatively 

 larger than in adult bone. After a few days, they become quite red and are better defined. 

 The canaliculi may also be traced. Under the periosteum giant-cells may be found here and 

 there. (Indicate the periosteum, the osteoblasts, and bone-corpuscles in PI. VI., Fig. 6.) 



DENSE DRY BONE. 



PREPARATION. Take a human radius which has been completely freed from grease ; with 

 a fret-saw cut a very thin transverse section. Grind the section on a hone moistened with water. 

 Examine with a low power to determine when the section has been ground thin enough. 

 Rinse it in water to get rid of the debris, and allow it to dry. Take Canada balsam, which is 

 quite hard in the cold, and place a small piece of it on a slide, gently warmed over the flame* of a 

 spirit-lamp till the balsam melts. Allow the balsam to cool, and before it has become quite 

 hard, place on it the section of bone, and cover. This method prevents the balsam from 

 getting into the lacunas and canaliculi, and so rendering the bone toe transparent. Make a 

 corresponding longitudinal section of the shaft of a long bone. 



.UNIVERSITY: 



T. S. OF DENSE DRY BONE. 



EXAMINATION (L). Observe the Haversian systems, each consisting of-jfr^-ffaversian 

 canal surrounded by lamellae disposed concentrically with relation to it Haversian lamellae ; 

 amongst these are seen the lacunas which resemble black dots with fine branches the 

 canaliculi proceeding from them. Observe also the circumferential or peripheric, and the 

 intersystemic or intermediary lamellae. 



(H). Observe the shape flattened ovals and arrangement of the lacunae ; they appear 

 black, being filled with air. From them proceed fine, branching canals, which appear as fine 

 black lines, running across the lamellae and uniting the lacunae by a network of very fine 

 tubes. The canaliculi of the outermost row of lacunae of any Haversian system do not 

 usually open into the lacunas of an adjoining system, but bend on themselves, and open into the 

 lacuna from which they sprang, or into an adjoining lacuna of the same system. These are 

 the so-called ' recurrent ' canaliculi (Ranvier). (Indicate t/te lacuna and canaliculi in PL VI., 

 Figs. 4 and 5.) 



L. S. OF DENSE DRY BONE. 



EXAMINATION (L). The Haversian canals are cut longitudinally or obliquely (with 

 transverse or oblique branches connecting them), and they open on the surface of the bone 



F 



