652 EMBRYOLOGY. 



37. Primary and secondary bones sometimes remain separate in 

 later stages, sometimes they fuse with each other to form bone- 

 complexes, like the temporale and sphenoidale. 



38. After the conclusion of the process of ossification only unim- 

 portant remnants of the primordial cranium persist as the carti- 

 laginous partition of the nose and as the nasal cartilages. 



C. The Skeleton of the Extremities. 



39. The skeleton of the limbs, excepting the clavicle, the develop- 

 ment of which exhibits many peculiarities, is established in the 

 cartilaginous stage. (Cartilaginous shoulder-girdle, cartilaginous 

 pelvic girdle, cartilages of arm and leg.) 



40. The ossification takes place, in the same manner as in the verte- 

 bral column and primordial cranium, from centres of ossification by 

 disintegration of cartilaginous tissue and its replacement by osseous 

 tissue. 



41. The most of the small cartilages of the wrist and ankle ossify 

 from a single bone-nucleus, but the larger flat cartilages of the 

 shoulder and pelvic girdles from several centres. 



42. The cartilaginous fundaments of the tubular [long] bones 

 ossify at first in the middle, which region is designated as diaphysis, 

 whereas their two ends the epiphyses remain for a long time 

 cartilaginous, and are the means of the elongation of the skeletal 

 element. 



43. In Man the cartilaginous epiphyses begin to ossify from centres 

 of their own (epiphysial nuclei), some of them in the last month 

 before, others not until after birth. 



44. The fusion of the bony diaphysis with the bony epiphyses does 

 not take place until the termination of the growth of the skeleton 

 and body in length, and is accompanied by the removal of the 

 intervening cartilaginous tissue. 



45. Before growth is at an end the tubular bones can be divided 

 into a larger middle piece (diaphysis) and two small bony epiphyses. 



46. Of the cartilaginous fundament of a tubular bone there is 

 preserved only a small remnant as a cartilaginous covering of the 

 articular ends (articular cartilage). 



47. The medullary cavity of the tubular bones is formed by the 

 resorption of the spongy bone-substance that first replaced the 

 cartilage. 



48. Whereas the articular ends of bones preformed in cartilage 

 -.are covered over with hyaline cartilage, the articular surfaces of 



