DEVELOPMENT OF THE OSSEOUS SYSTEM. 



in the orang. All of the carpal bones are still cartilaginous at birth. They ossify 

 as follows: Os magnum unciform (first year), cuneiform (third year), trapezium, 

 semilunar (fifth year), scaphoid (sixth year), trapezoid (seventh year), pisiform 

 (twelfth year). 



The metacarpal bones exhibit a center in the diaphysis at the end of the third 

 month; the same is true of the phalanges. All of the phalanges and the first 

 bone of the thumb have cartilaginous epiphyses at the proximal extremity; the 

 remaining metacarpal bones at the distal extremity. Accordingly, the first 

 bone of the thumb is to be regarded as a phalanx. The epiphyses of the meta- 

 carpal bones ossify in the second year; those of the phalanges in the third year; 

 union takes place at the time of puberty. The assertion of Schenk is noteworthy, 

 that in the first formation a greater number of fingers (up to nine) are indicated, 

 which later diminish to five. Accordingly, polydactyly may be regarded as a 

 malformation due to arrest of development. Moreover, rudimentary indications 

 of a sixth finger (radial aspect) and of a sixth toe (tibial aspect) are present in 

 many mammals, for example in moles, v. Bardeleben designates them respect- 

 ively prepollex and prehallux, They are rare in man as an animal analogue. 



The innominate bone, in the cartilaginous stage, consists of two parts, the 

 pubis and the ischium. Ossification begins at three centers: One in the ilium 



(between the third and fourth 

 months), one in the descending 

 ramus of the ischium (between 

 the fourth and fifth months), 

 one in the horizontal ramus of 

 the pubis (between the fifth and 

 seventh months). Between the 

 sixth and the fourteenth year 

 three centers appear where the 

 bodies of the three bones unite 

 to form the acetabulum ; another 

 in the superficies auricularis and 

 one in the symphysis. Further 

 accessory centers are as follows: 

 One each in the anterior inferior 

 spine, the crest of the ilium, the 

 tuberosity and spine of the 

 ischium, the spine of the pubis, 

 the iliopectineal eminence and 

 the floor of the acetabulum. The 

 descending ramus of the pubis 

 and the ascending ramus of the 

 ischium are the first to unite be- 

 tween the seventh and eighth 

 years. The Y-shaped suture in 

 the acetabulum persists until 

 puberty. A special center in the 

 margin of the acetabulum appears 

 as the os acetabuli (twelfth year) , 

 which fuses with the adjacent 

 bones in the eighteenth year. 



The femur acquires its mid- 



le center of ossification at the end of the second month. At birth there is a 

 :nter n the lower epiphysis, and somewhat later one in the head. 



I here are in addition: One in the greater trochanter (between the third and 



;h years) one in the lesser trochanter (between the thirteenth and fourteenth 



s), two in the condyles (between the fourth and eighth years). Union of all 



occurs at about the time of puberty. The patella is a sesamoid bone in the tendon 



ol the quadriceps femoris. In some marsupials it unites with the fibula as the 



olecranon. The patella is cartilaginous in the second month; it ossifies 



between the first and third years. 



and S 6 fi !^ la under g ossification in their diaphyses at the beginning 

 ? he Up ? er ^Vsis fi rst contains a center (between the 

 nf ^ * hen u the ^wer. Accessory centers are present in the tuber- 



osity of the tibia and m the malleoli. Consolidation of all takes place at puberty. 

 ; tarsal bones are formed in a manner analogous to those of the carpus: 



FIG. 383. Ossification of the Innominate. 



