72 



ZOOLOGY. 



Fig. 86. PLAN OF IDEAL GIRDLE AND LIMB. 



begin with the girdle is cartilage, but when this is ossified 



(i.e. replaced by cartilage- bone) each of these three portions 



(dorso-lateral, antero-ventral and postero-ventral) forms a 



separate bone (all 

 paired). The limb- 

 skeleton is divided 

 into four parts a 

 proximal, consisting 

 of one long bone ; the 

 next, of two side by 

 side; then comes a 

 series of small bones, 

 in three rows of three, 

 one, and five respect- 

 ively (see fig. 36) ; and finally five radiating rows (digits) 



of rod-like bones. In the primitive position, the limb 



points out at right angles to the body 



and the digits all lie in the horizontal 



plane: this may be imitated on the 



human arm, if the reader will hold it 



out at right angles to the side of the 



body with the thumb upwards (i.e. 



forwards) and the palm of the hand 



forwards (i.e. ventralwards). In this 



position the arm can only be bent 



ventralwards, so the ventral surface is 



called the flexor surface, and the dorsal 



the extensor. Looking at the limb 



from the ventral side (fig. 36) we call 



the forward edge preaxial, the hinder 



edge postaxial : these same terms can 



be applied to distinguish the two 



bones of the second segment of the 



limb, and also to express the relative < The , sha i ie . i t t , 8lig , bt 1 1 7 N dif ' 



. '. - i -i T ferent in the adult.) 



positions or the several digits. In 



numbering the digits we begin with the most preaxial 



one. So much for the general plan. 



10. The Shoulder-girdle, or Pectoral Girdle, in the 

 rabbit is decidedly incomplete. Only the dorso-lateral bone 



Fig. 37. SCAPULA OF A 

 YOUNO RABBIT. 



