GENERAL AXATOMY OF BONE. 39 



of ossification is called intra-cartila.ginous, to distinguish it from that which takes 

 place in a membranous tissue, quite different in its nature from cartilage. The 

 latter mode of ossification is called intra-membranous. Examples of it are seen, 

 according to Kolliker, in the upper half of the expanded portion of the occipital 

 bone ; the parietal and frontal bones ; the squamous portion and tympanic ring of 

 the temporal bone ; the internal lamella of the pterygoid process of the sphenoid ; 

 the cornua sphenoidalia ; in all the bones of the face, excepting the inferior turbi- 

 nated ; and, according to Brack, in the clavicle. 



The period of ossification is different in different bones. The order of succes- 

 sion may be thus arranged (Kolliker) : 



In the second month, first, in the clavicle, and lower jaw (fifth to seventh week) ; 

 then, in the vertebra, humerus, femur, the ribs, and the cartilaginous portion of 

 the occipital bone. 



At the end of the second, and commencement of the third month, the frontal 

 bone, the scapula, the bones of the forearm and leg, and upper jaw, make their 

 appearance. 



In the third month, the remaining cranial bones, with few exceptions, begin to 

 ossify, the metatarsus, the metacarpus, and the phalanges. 



In the fourth month, the iliac bones, and the ossicula auditus. 



In the fourth or fifth month, the ethmoid, sternum, pubis, and ischium. 



From the sixth to the seventh month, the calcaneum, and astragalus. 



In the eighth month, the hyoid bone. 



At birth, the epiphyses of all cylindrical bones, occasionally with the exception 

 of those of the femur and tibia ; all the bones of the carpus ; the five smaller 

 ones of the tarsus ; the patella ; sesamoid bones ; and the last pieces of the coccyx, 

 are still unossified. 



From the time of birth to the fourth year, osseous nuclei make their appearance 

 also in these parts. 



At twelve years, in the pisiform bone. 



The number of ossific centres is different in different bones. In most of the short 

 bones, ossification commences by a single point in the centre, and proceeds towards 

 the circumference. In the long bones, there is a central point of ossification for the 

 shaft or diaphysis ; and one or more for each extremity, the epiphyses. That for the 

 shaft is the first to appear ; those for the extremities appear later. For a long period 

 after birth, a thin layer of unossified cartilage remains between the diaphysis and 

 epiphyses, until their growth is finally completed, their junction taking place either 

 at the period of puberty, or towards the end of the period of growth. The union of 

 the epiphyses with the shaft takes place in the inverse order to that in which their 

 ossification began ; for, although ossification commences latest in those epiphyses 

 towards which the nutritious artery in the several bones is directed, they become 

 joined to the diaphyses sooner than the epiphyses at the opposite extremity, with 

 the exception of the fibula, the lower end of which commences to ossify at an 

 earlier period than the upper end, but, nevertheless, is joined to the shaft earliest. 



The order in which the epiphyses become united to the shaft appears to be 

 regulated by the direction of the nutritious artery of the bone. Thus the arteries 

 of the bones of the arm and forearm are directed towards the elbow, and the 

 epiphyses of the bones forming this joint become united to the shaft before those 

 at the opposite extremity. In the lower extremities, on the contrary, the 

 nutritious arteries pass in a direction from the knee; that is upwards in the femur, 

 downwards in the tibia and fibula ; and in them it is observed, that the upper 

 epiphysis of the femur, and the lower epiphyses of the tibia and fibula, become 

 first united to the shaft. 



Where there is only one epiphysis, the medullary artery is directed towards that 

 end of the bone where there is no additional centre : as, towards the acromial end 

 in the clavicle ; towards the distal end of the metacarpal bone of the thumb and great 

 toe; and towards the proximal end of the other metacarpal and metatarsal bones. 



A knowledge of the exact periods when the epiphyses become joined to the 



