776 DIRECTIONS FOB LABORATORY WORK 



(canal and lamellae) ; lacunae, and canaliculi. Sketch (77) a complete 

 Haversian system. What are the contents of the Haversian canal? 

 What is the structure of the osseous lamellae ? Content of lacuna? ? Sig- 

 nificance of canaliculi? Study a fragment of a ground longitudinal 

 section of the shaft (diaphysis) of a long bone. Sketch (78) a Haver- 

 sian canal at the point of branching, with the enveloping lamellae. Note : 

 Volkman's canals of the circumferential and interstitial lamellae. Are 

 the latter connected with the Haversian systems? Do the Haversian 

 systems connect with the periphery and the central marrow cavity? 

 What are the nutrient foramina of a bone ? How many to the shaft of 

 a long bone? to an epiphysis? 



(3) DECALCIFIED COMPACT BONE. Study stained longitudinal 

 section of end of long bone including epiphysis and part of dia- 

 physis. Note: periosteum, muscle attachments, fibers of Sharpey, 

 Haversian systems, bone cells, endosteum, marrow. Sketch (79) typical 

 areas from epiphysis (cancellous bone) and diaphysis (compact bone), 

 and periosteum. 



(4) BONE DEVELOPMENT. 



(a) ENCHONDRAL OSSIFICATION (Substitution Bone). Study a lon- 

 gitudinal stained section of a decalcified small fetal long bone (e.g., pha- 

 lanx of finger, or metacarpal; or some small bone of fetal pig). Sketch 

 (80) l.p. a narrow strip of section through center of ossification and in- 

 cluding terminal articukr cartilage and central marrow cavity. This 

 drawing should illustrate the successive stages in the process of enchond- 

 ral ossification. Sketch (81) h.p. a strip through area of ossification. 

 Note : calcified cartilage remnants and adjacent rows of disintegrating 

 cartilage cells; primary marrow spaces; periosteal bone; spicules of pri- 

 mary bone; and epiphyseal line of cartilage? Sketch (82) : (a) perios- 

 teum; (b) strip of periosteal bone, including a periosteal bud of osteo- 

 genic tissue within a Haversian space (the precursor of a Haversian sys- 

 tem) ; (c) plate of enchondral bone with central calcified cartilage core 

 and surface layer of primordial bone, bone cells, bone lacunae, and peri- 

 pheral osteoblasts and asteoclast (in a Howship's lacuna) ; (d) primor- 

 dinal marrow areola with marrow cells, including blood cells, osteoblasts 

 and giant cells (megakaryocytes and polykayocytes osteoclasts). 



(b) INTKAMEMBRANEOUS OSSIFICATION. Study stained section of 

 jaw of some mammalian fetus (e.g., of pig fetus of about 35 mm.) for 

 developing membrane bone (cancellous bone). Sketch (83 a) small 

 area of core of plate. Sketch (83 b) an osteoclast, noting the con- 

 tent of resorbed bone globules. 



