C66 



SKELETON. 



G*, H*), while the pisiform bone (q) of the 

 hand corresponds in position to the os calcis 

 (</) of the foot. 



While it appears, therefore, an undeniable 

 truth that that aspect of the fore-limb (B, C,D), 

 which we commonly call the front, is in reality 

 structurally identical with the back of the 

 lower member (F*, G*, n*), whereas the front 

 of the latter organ (F, G, H) is the structural 

 homologue of the back of the upper limb 

 (B*, c*, D*), let us examine closely into the 

 cause of this singular difference between both 

 organs. Anatomists have long since remarked 

 upon the singular twisted form of the hu- 

 merus. Cruveilhier speaks of the " groove of 

 torsion directed obliquely downwards and for- 

 wards " on thehumerus. This fact of torsion 

 in the shaft of the humerus I consider as 

 fully explaining the above mentioned pecu- 

 liarities which distinguish the upper from the 

 lower member. In primitive construction 

 both members are identical ; but this secondary 

 modification, viz. the torsion of the humerus, 

 is that circumstance which distinguishes them 

 one from the other. 



While, in idea, I untwist the hnmerus by 

 bringing its back to the front, I at the same 

 time unravel the gordian knot of that problem 

 which has so long existed as a mystery for 

 the homologist. 



The back of the humerus (B*) presents a 

 smooth and rounded form, like the front of the 

 femur (F). If, in idea, I twist the femur (F) 

 in its long axis, so as to bring its back to the 

 front, then F* makes its linea aspera (/) per- 

 form a spiral curve forward, just as the spiral 

 rough line (/) on the shaft of the humerus 

 (B) manifests its own contorted character ; 

 and at the same time I bring the points 

 (,a, k,l), usually on the back of the lower end 

 of the femur, forward, like the corresponding 

 points (gje,l) of the humerus (B). If, again, 

 in idea, I untwist the humerus (B) in its long 

 axis, so as to bring its back to the front, then 

 B* uncoils its rough spinal line, and gives this 

 line its primitive vertical direction, similar to 

 what the linea aspera of the femur normally 

 presents, at the same time that the points 

 (/, //, i, /c) usually at the back of the humerus 

 (B*) are brought forwards like the points 

 (/, //, i, /f) of the femur (F). 



Injfig. 485. I have drawn both limbs, each 

 in its front and back aspect, on either side of 

 the common median line. When the reader 

 will compare B, c, D with F, G, H, in reference 

 to this line, he will find that though the ulna 

 (c) approaches this median line like the tibia 

 (H), yet that this position does not render 

 both these bones structurally homologous ; 

 for, from the foregoing remarks in reference to 

 the twisted condition of the limb (B, c, D), he 

 must have learned that it is owing to this 

 fact of torsion that the bone (c) (ulna) holds, 

 in reference to the median line, the position of 

 (H) the tibia, with which latter the ulna is 

 not homologous. When we, in idea, untwist 

 n, and bring it into the position of B*, then 

 the radius (D*) comes into sidelong position 

 with the median line, like the tibia (H) ; and 



now both these bones manifest their homolo- 

 gous character, as well in position as in 

 general form. The hand and the foot are, 

 also, by these movements made to corre- 

 spond. Is it not a fact of singular interest, 

 so far as it explains the law of nature in exer- 

 cising these special modifications on the struc- 

 turally identical fore and hind limbs, that 

 when, in reference to the common median 

 line, we untwist B,D, c to the position B*, D*, 

 c*, we then render this latter of the same 

 aspect, compared with the ideal twisted con- 

 dition of F*,G*,H*, as the figure F,G,H com- 

 monly manifests compared with B, D, c ? 



While we bear in mind the foregoing ex- 

 planation of the presential characters of the 

 upper and lower extremities, we are enabled 

 fully to recognise the homological relations of 

 these two members, as well when viewing 

 their several constituent parts as when con- 

 sidering them as whole or entire organs. 



The coracoid process a of the scapula A 

 answers to the anterior inferior spinous pro- 

 cess a of the iliac bone E ; the acromion pro- 

 cess b of A to the obliterated process b of E ; 

 the head of the humerus c of B, and both its 

 tuberosities e d, to the head c and trochanters 

 ed of the femur F; the rough spiral line/of B 

 to the linea aspera/ of F ; the outer condyle k 

 of B to the inner condyle / of F ; for it is owing 

 to the twist of the humerus B that the con- 

 dyle k lies outermost ; the olecranon process 

 h of B* to the patella h of F, the twist of the 

 humerus explaining why the former part is at 

 the back and the latter in front ; the radius 

 D on the outer aspect of the foramen to H, 

 the tibia on the inner side of the leg, the 

 twist in the arm-bone explaining this differ- 

 ence as to their position, and also why the 

 ulna (c) lies at the inner side of the arm, 

 while its homologue (G) the fibula appears at 

 the outer side of the leg. I shall here leave 

 the reader to pursue the thread of this subject 

 as far as he feels inclined ; for the first and 

 radical difficulty being removed allows the 

 subject to be easily followed through its se- 

 condary stages.* 



The fore-limbs of all species of animals are 

 similar to one another in all respects save 

 that of quantity, and this quantitative differ- 

 ence is manifested chiefly upon the distal 

 extremities. The obliteration of one or more 

 parts of the distal organ renders it in the 

 varying conditions of those forms to which we 

 give the names of hands, paws, wings, palms, 

 talons, hoofs, &c ; the same law of degrada- 

 tion is exercising on the distal extreme of the 



* Vicq d'Azyr believed that the ulna represented 

 the tibia, and the radius the fibula. M. de Blain- 

 ville, on the contrary, regarded the tibia and the 

 radius as homologous. Cruveilhier considered that 

 neither of the bones of the fore-arm resembled, by 

 itself, one of the bones of the leg, and therefore in- 

 clines to the belief that it is the upper end of the 

 tibia which represents the upper half of the ulna, 

 while the lower half of the tibia represents the 

 lower half of the radius ; moreover, that the fibula 

 is represented by the upper half of the radius and 

 the lower half of the ulna. See " Anatomic Descrip- 

 tive," t. i. p. 315. 



