50 THE ANATOMY OF VERTEBRATED ANIMALS. 



liquely from the post-axial condyle of the humerus to the radi- 

 us. In the hind-limb, a corresponding muscle, the poplitmiis^ 

 proceeds from the post- axial condyle of the femur to the tibia. 

 The pronator quadratus^ which passes from the ulna to the 

 radius, has its analogue, in some MarsupiaUa and B,eptilia^ 

 in muscles which extend from the fibula to the tibia. 



The Muscles of the Digits. — The remaining muscles of the 

 two limbs are, primarily, muscles of the digits, and are at>- 

 tached either to the basi-digital (metacarpal or metatarsal) 

 bones, or to the phalanges, though they may acquire second- 

 ary connections with bones of the tarsus or carpus. The 

 plan upon which they are arranged, when they are most com- 

 pletely developed, will be best understood by commencing 

 with the study of their insertion in any one of those digits 

 which possesses a complete set ; such, for example, as the 

 fifth diofit of the manus, or little fino-er, in Man and the hi^^rher 

 Primates. 



On the dorsal aspect this digit presents : first, attached to 

 the base of its metacarpal bone, the tendon of a distinct mus- 

 cle, the extensor carpi ulnaris. Secondly, spreading out over 

 the phalanges into an aponeurosis, which is principally at- 

 tached to the first and second, is a tendon belonging to another 

 muscle, the extensor rninhni digiti. Thirdly, entering the same 

 expansion is one tendon of the extensor communis digitoruyn. 



On the 'central aspect there are : first, attached to the base 

 of the metacarpal, the tendon of a distinct muscle, the jfexor 

 carpi ulnaris / secondly, arising from the sides and ventral face 

 of the metacarpal, and inserted into either side of tlie base of 

 the proximal phalanx, two muscles, the inter ossei j thirdly, 

 inserted into the sides of the middle phalanx by two slips, a 

 tendon of the flexor perforatus / and fourthh^, passing be- 

 tween these two slips, and inserted into the base of the distal 

 phalanx, a tendon of the flexor perforans. Thus there are 

 special depressors, or flexors, for each segment of the digit. 

 There appear, at first, to be but three elevators, or extensors, 

 but, practically, each segment has its elevator. For the ten- 

 dons of the extensor communis and extensor minimi digiti are 

 attached to the middle and the proximal phalanges ; and the 

 distal plialanx is specially elevated by tlie tendons of two lit- 

 tle muscles, which, in Man, are usually mere subdivisions of 

 the interossei, and pass upward, joining the extensor sheath, 

 to be finally inserted into the distal phalanx. 



The fifth digit of the pes, or little toe, sometimes presents 

 the same disposition of muscles, namel}" : 



