122 MORPHOLOGY OF THE BOXES OF THE LIMBS. 



in tlie 2nd year. The anterior tuberosity is occasionally fonned from a separate 

 centre. The lower epiphysis and sliaft nnite in the ISth or I'Jth year, the upj^er 

 epiphysis and shaft unite in the 21st or 22nd year. In the fibula the centre for 

 the shaft ajii^ears rather later than in the tibia ; that for the lower extremity 

 appears in tlie 2nd year, and that for the upper, unlike that of the tibia, not till 

 the 3rd or 4th year. The lower epiphysis and shaft unite about the 21st year, 

 the upper epiphysis and shaft unite about the 24th year. 



Tlie tuv.siil honcx are ossified in cartilage each from a single nucleus, with the 

 exception of the os calcis, which in addition to its proper osseous centre, has an 

 epiphysis upon tlie upper part of its posterior extremity. The principal nucleus 

 of the OS calcis apjiears in the fith month of foetal life ; its epiphysis begins to- 

 be ossified in the lOtli year, and is united to the tuberosity in the inth or l(]th 

 year. The nucleus of the astragalus appears in the 7th month ; that of the 

 cuboid at bii-th ; that of the external cuneifonii in the 1st year ; that of the 

 inteiTial cuneiform in the Srd year ; that of the middle cuneifonn in the 4th 

 year ; and that of the scaphoid in the 4 th or 5th year. 



The mi-tatar.siil honc.t and j>Jitila)i//rs agree respectively with the con-esponding 

 bones in the hand, in the mode of their ossification. Each bone is formed from 

 a piincipal piece and one epiphysis ; and while in the four outer metatarsal bones 

 the epiphysis is at the distal extremity, in the metatarsal bone of the great toe 

 and in the phalanges it is placed at the proximal extremity. In the first meta- 

 tarsal bone there is also to be observed, as in the fii'st metacaiiial (see ossification 

 of that bone), a tendency to the formation of a second or distal epiphysis. (A. 

 Thomson.) In the metatarsal bones the nuclei of the shafts appear in the 8th 

 or 9th week. The epiphyses appear from the 3rd to the 8tli year, and unite with 

 the shafts from the 18th to the 20th year. The nuclei of the shafts of the 

 phalanges appear in the 9th or 10th week. The epiphyses appear from the 8th to 

 the 10th year, and unite with the shafts from the 19th to the 21st year. 



MORPHOLOGY OF THE BONES OP THE LIMBS- 



Relation to the Axial Skeleton. — Anatomists have generally agi'ced to look 

 upon the relation which the bones of the limbs bear to the rest of the skeleton 

 as that of appendages to the trunk, hence their distinction as fipj^'/uJiriilar jiarts 

 of the /hritil, skeleton ; and most are also disposed to regard these appendages as 

 similar radiations or extensions from one or more of the vertebral segments in two 

 determinate situations of the tnink. But opinions are still di\aded as to the tji^ical 

 number of the vertebral somatomes which are involved, and as to the exact nature 

 of the parts which fonii the radiations. The existence in both of a supporting 

 arch in relations somewhat resembling those of pleurapophyses or riljs, and the 

 division of this arch at the joints of the limbs (shoulder and hip joints) into an 

 upper or dorsal and a lower or ventral section is easily recognised ; the dorsal 

 being fimily attaclied to the side of the sacrum in the lower limb, Avhile in the 

 upper, the ventral part of the arch abuts on the sternum. But it does not appear to 

 be yet deteniiined. even in the case of the pelvic arch, what is the exact natiu-e of 

 the lateral mass of the sacrum, and in both limbs it is stiU doubtful what is the 

 precise homological relation of the arch to the vertebrte. The fact, however, 

 that a quiiiquifid division of the peripheral parts of both limbs is constant in 

 man and a certain number of animals, and that in no animals above fishes is 

 there a greater number of elements than five, while in many animals some of the 

 elements may be absent or abortive, together with the remai-kably regular passage 

 of a certain numlier of sj^inal nen'es from the tiaink to the limb, of which five 

 are of considerable size in man and those animals possessing the limb elements 

 complete, appears favourable to the view that both limbs have prolonged mto 

 them the elements of five vei-tebral segments, and it is generally held that these 

 elements follow each other in a similar order in the two limbs from the cephalic 

 to the caudal part of the vertebral axis, so that the poUex and radial elements 

 occupy the cephalic side of the upper, while the hallux and tibia take the same 

 place in the lower limb. (See Owen " On the Nature of Limbs," Goodsir '• On. 

 the Moi'iihological Constitution of Limbs," in Edin. Xew Philos. Joum., 1857.) 



