COMPAEISOX OF ARM AXD LEG BOXES. 



127 



Compar. des IMembres Peh-iens et Thoraciqucs, &c.. deduite de la Torsion de 

 rHumerus," Mem. de TAcad. de Montpellier, torn, iii., 1857. Gegenbaur, " On 

 the Torsion of the Humerus,' in Jenaischen Zeitsch. and Annal. des Sciences 

 Nat., iv.. p. 50.) But it is easy to show by reference to the embryonic condi- 

 tion, that the outward displacement of the lower end of the humerus in the xiro- 

 gress of its formation, does not exceed 90". 



Martins has also i^roposed the view, that in order to compare the lower le"- 

 •with the fore-arm, it is necessary to look upon the upper part of the tibia (coitc- 

 sponding in the main to the radius), as including, or having had transfeiTed to 

 it as it were, the olecranon jirocess and upper jjart of the ulna ; and he thus 

 accounts for the attachment of the great extensor tendon of the leg to the tibia 

 through the x^^tella, which, according to his scheme, represents the olecranon 

 instead of to the fibula. Ingenious as these views undoubtedly are, they are 

 liable to considerable objections on embiyological grounds, and though not to 

 be rejected altogether, cannot be considered as suppljong the key to the explana- 

 tion of the liomologies of the limbs. 



Hand and Foot.— The similaritj- of the digital and metacai-pal bones of the 

 hand with those of the foot in number, form, and connections is so great that 

 the homological correspondence of these bones is immediately recognised. The 

 main differences between them consist in the greater general length of the digits 

 of the hand, and the opposability of the thumb to tlie other fingers through 

 its mobility at the caqio-metacarpal articulation, — conditions which are peculiarly 

 ■characteristic of man. and do not exist in the same fonn or degree in any of the 

 lower animals. 



Pig. 113. — Dorsal Surface of the Right Manus of Fig. 113. 



A Water Tortoise. (Flower after Gegenbaur. ) 



R, i-adius ; U, ulua ; r, radiale ; /, intermedium ; 

 M, ulnare ; c, centrale ; 1 — 5, five carpal bones of the 

 distil row ; m' — J(i^, five metacarpals. 



Between the carpus and tarsus there is also 

 considerable general similarity, especially in the 

 bones of the distal series ; but in those of the 

 l^roximal row there are some differences which 

 maj' he referred to here at greater length. There 

 can, indeed, be no doubt as to the homological 

 con'cspondence of the trapezium, trapezoid and 

 magnum with the internal, middle and external 

 cuneifoiin bones of the tarsus respectively, nor of 

 the unciform with the cuboid bone ; and all the 

 more in the case of the last two bones, that it is 

 found that in the Chelonia and some other reptiles 

 and amphibia, the second series of carpal and 



tarsal bones are increased to five by the division of the unciform of the hand 

 and cuboid of the foot into two each ; thus giving one carj^al or tarsal bone 

 for articulation with each of the five metacarpal or metatarsal bones. 



Upon the homologies of the proximal series of bones, new light has been 

 thrown by the researches of Gegenbaur. (" Untersuch. zur Vergleich. Anat., 

 kc. Carpus and Tarsus," Leipzig, 18G-1.) In the simplest and most constant 

 forai of this series in the carpus, he distinguishes typically three bones, viz., 

 a ntdidl, an intcrmcdidfc, and an itlnar, corresponding respectively to the scaphoid, 

 lunar and cimeiform bones of human anatomy. The pisiform he regards as an 

 osseous element developed in the tendon of a muscle (flexor carpi ulnaris), 

 and therefore not holding the same rank in the series as the other bones, 

 but constituting an ulnar scmmoid. In the foot Gegenbaur shows that the 

 axtrat/iihis coiTesponds to the united scaphoid and lunar of the hand, or to 

 the proximal parts at least of these bones. But in some mammals (Simiae and 

 Ptodentia), as well as in reptiles and amphibia, another bone has long been known 



