DEVELOPMENT OF THE BONES OF THE LIMBS. 



88l 



the upper epiphysis, and one in the capitellum (1st year) ; one in the great tuberosity and one 

 in the small tuberosity (2nd year) ; two in the condyles (5th to 10th year) ; one in the trochlea 

 (12th year). The epiphyses unite with the shaft at the 16th to 20th year. 



The radius ossifies in the shaft at the 3rd month. The other centres are one in the lower 

 epiphysis (5th year), one in the upper (6th year), and an inconstant one in the tuberosity, and 

 one in the styloid process. They unite at puberty. 



The ulna also ossifies in the shaft at the 3rd month. There is a centre in the lower end 

 (6th year), two in the olecranon (11th to 14th year), and an inconstant one in the coronoid 

 process, and one in the styloid process. They consolidate at puberty. 



The carpus is arranged in mammals in two rows. The first row contains three bones the 

 radial, intermediate, and ulnar bones. In man these are represented by the scaphoid, semi- 

 lunar, and cuneiform bones ; the pisiform is only a sesamoid bone in the tendon of the 

 flexor carpi ulnaris. The second row really consists of as many bones as there are digits (e.g., 

 salamander). In man the common position of the 4th and 5th fingers is represented by the 

 unciform bone. Morphologically, it is interesting to observe that an os centrale, corresponding 

 to the os carpale centrale of reptiles, amphibians, and some mammals, is formed at first, but 

 disappears at the 3rd month, or unites with the scaphoid. Only in very rare cases is it 

 persistent. All the carpal bones are cartilaginous at birth. They ossify as follows : Os 

 magnum, unciform (1st year), cuneiform 

 (3rd year), trapezium, semilunar (5th year), 

 scaphoid (6th year), trapezoid (7th year). 

 and pisiform (12th year). 



The metacarpal bones have a centre in 

 their diaphyses at the end of the 3rd 

 month, and so have the phalanges. All 

 the phalanges and the first bone of the 

 thumb have their cartilaginous epiphyses 

 at the central end, and the other metacarpal 

 bones at the peripheral end,* so that the 

 first bone of the thumb is to be regarded 

 as a phalanx. The epiphyses of the meta- 

 carpal bones ossify at the 2nd, and those 

 of the phalanges at the 3rd year. They 

 consolidate at puberty. 



The innominate bone, when carti- 

 laginous, consists of two parts the pubis 

 and the ischium (Rosenberg). Ossification 

 begins with three centres one in the ilium 

 (3rd to 4th month), one in the descending 

 ramus of the ischium (4th to 5th month), 

 one in the horizontal ramus of the pubis 

 (5th to 7th month). Between the 6th to 

 the 14th year, three centres are formed 

 where the bodies of the three bones meet 

 in the acetabulum, another in the super- 

 ficies auricularis, and one in the symphysis. 



Other accessory centres are : One in the ^.^ 



anterior inferior spine, the crests of the " 



ilium, the tuberosity and the spine of the Centres of ossification of the innominate bone, 

 ischium, the tuberculum pubis, eminentia iliopectinea, and floor of the acetabulum. At first 

 the descending ramus of the pubis and the ascending ramus of the ischium unite at the 7th 

 to 8th year; the Y-shaped suture in the acetabulum remains until puberty (fig. 674). * } Spf 



The femur has its middle centre at the end of the 2nd month. At birth, there is a centre in 

 the lower epiphysis ; slightly later in the head. In addition, there is one in the great 

 trochanter (3rd to 11th year), one in the lesser trochanter (13th to 14th year), two in the con- 

 dyles (4th to 8th year) ; all unite about the time of puberty. The patella is a sesamoid bone in 

 the tendon of the quadriceps femoris. It is cartilaginous at the 2nd month, and ossifies from 

 the 1st to the 3rd year. 



The tarsus generally resembles the carpus. The os calcis ossifies at the beginning of the 7th 

 month, the astragalus at the beginning of the 8th month, the cuboid at the end of the 10th, 

 the scaphoid (1st to 5th year), the I. and II. cuneiform (3rd year), and the III. cuneiform (4th 

 year). An accessory centre is formed in the heel of the calcaneum at the 5th to 10th year, 

 which consolidates at puberty. 



The metatarsal bones are formed like the metacarpals, only later. 



[Histogenesis of Bone. The great majority of our bones are laid down in cartilage, or are 

 preceded by a cartilaginous stage, including the bones of the limbs, backbone, base of the skull, 

 sternum, and ribs. These consist of solid masses of hyaline cartilage covered by a membrane, 



3k 



674. 



