'!.] GENERAL VIEW OF INTERNAL SKELETON. 231 



all directed outwards, the thumb being turned forwards (pre- 

 axially), and the little finger of course at the opposite side of 

 the hand. The arm being placed in this position, and a line 

 drawn from the limb root to the tip of the middle finger, 

 all that is in front (man being supposed to be in the hori- 

 zontal attitude of a quadruped) of such a line is called 

 pre-axial, all that is behind it post-axial, directions corre- 

 sponding with those already indicated by the same term 

 with regard to the backbone. 



20. The skeleton of the fore-arm and hand is divisible into 

 a. tri- and a bi-digital series, placed side by side. 



Thus there is, first, the radius ; the scaphoides and lunare ; 

 the trapezium, the trapezoides, and the magnum ; the first, 

 second, and third metacarpals ; and the annexed digits 

 forming the tri-digital series. 



We have, secondly, the ulna ; the cuneiforme ; the fourth 

 and fifth metacarpals ; and the corresponding digits form- 

 ing the bi-digital series. 



Such being some of the leadirg points in the skeletal struc- 

 ture of the pectoral or thoracic limbs, what now are the 

 resemblances to them exhibited by the pelvic limbs, and 

 what the differences? 



21. The pelvic limbs in man are suspended, as we have 

 seen, from a complete bony girdle firmly attached to the 

 backbone on the dorsal aspect, its two sides meeting together 

 uninterruptedly (at the pubic symphysis) on the ventral aspect. 



FIG. 199. Transverse Section of the Pelvic Region of Man, showing the relation 

 borne by the appendicular skeleton (ossa innominata) to the axial skeleton : 

 the latter is represented by the black parts of the figure. 



, neural canal ; s, neural spine ; ac, abdominal cavity ; /, pubis ; sy t symphysis 

 of the pubes ; il, ilium ; f, head of the femur. 



Here, then, we have a great difference between the limb- 

 girdles. This however disappears when man's pelvic girdle is 

 compared with the pectoral girdle of the Ray (R. clavata), 

 which is similar to the human pelvis in its relations to the 

 axial system ; while in most Fishes the pelvic girdle is com- 

 plete below only, but not at all above, thus resembling the 

 pectoral girdle of man. 



Instead of a union on the ventral aspect by the intervention 



