72 



GENERAL ZOOLOGY 



much reduced; a pentadactyl hand and foot, and a plantigrade 

 foot posture. Of the larger mammals, bears alone have planti- 

 grade feet. 



The skeleton of the limbs of birds in the course of evolution 

 has undergone considerable modification (Fig. 44). In the wing 



Fig. 44. — Skeleton of trunk and appendages of domestic fowl. 1, cervical rib; 

 2, ilium; 3, ischium; 4, pubis; 5, pygostyle; 6, ilio-sciatic foramen; 7, uncinate 

 process of thoracic rib; 8, humerus; 9, ulna; 10, radius; 11, ulnar carpal; 12, meta- 

 carpal of ulnar digit; 13, coracoid; 14, sternum; 15, metasternum; 16, hypoclei- 

 dium; 17, clavicle; 18, femur; 19, fibula; 20, tibiotarsus; 21, tarsometatarsus; 22, 

 metatarsus of first digit. I, II, III, IV, V, digits. The digits of the fore limb 

 should be labeled II, III and IV instead of III, IV and V respectively. 



of the domestic fowl, ulna and radius are both present, the ulna 

 being the larger. Carpals and metacarpals are reduced by 

 fusion. Of the metacarpals, II, III, and IV can be identified, and 

 adjoining these are the corresponding rudimentary digits. The 

 proximal element of the skeleton of the hindlimb is the femur. 

 The next segment consists of a very much reduced fibula and a 

 long cylindrical iibiotarsal bone, formed by fusion of the tibia 



