PROCESS OF OSSIFICATION. 107 



salt solution if recent, and the skin and muscular 

 layers are torn away from the outside and the dura 

 mater and cartilaginous layer (which in these animals 

 rises up laterally from the cartilaginous hasis cranii) 

 from the inside. The membrane in which the bone 

 is being formed is then left. It is held upon a glass 

 slide with a needle or line forceps, and brushed 

 firmly with a camel-hair pencil, the hairs of which 

 have been cut off short so as to render the stump 

 stiff and resisting. The piece must be kept wet, 

 and examined from time to time with a low power 

 to see whether the edges of the newly-formed bone 

 are sufficiently clear of the membrane and corpuscles, 

 so that the osseous spicules and their fibrous pro- 

 longations are readily seen. When this is the case 

 the piece is held with the forceps and well rinsed in 

 water or salt solution to free it from loose particles 

 of the soft tissue ; it is then placed in logwood solu- 

 tion, and when sufficiently colored (two or three 

 minutes) is mounted in glycerine. The osteoblasts 

 will be found stained by the logwood ; the ossified 

 part is dark and highly refracting, the osteogenic 

 fibres by which it is prolonged remain clear and 

 colorless. 



The process of intra-membranous development 

 may also be very advantageously studied in sections 

 of the lower jaw of the foetus or young animal, as 

 will be afterwards pointed out in describing the 

 mode of preparing this to show the development of 

 other structures, the teeth and hair, for example. 



Preparation 8. Development of bone in 

 cartilage, To study the mode of ossification in 

 cartilage it is not necessary to have recourse to the 

 bones of a fcetal animal, since any which are still in 

 process of growth will serve the same end, and it is 

 more convenient for purposes of manipulation if 

 they have attained a certain size. The long bones 

 of a new-born kitten may advantageously be em- 

 ployed, and the best preparations are certainly those 

 obtained from the recently killed animal, although 



