44 MAMMALIAN ANATOMY 



To the axial skeleton is attached, either directly by joints or 

 indirectly by muscles, the appendicular skeleton or framework of 

 the limbs. 



The axial skeleton is formed of one hundred and thirty-six bones, 

 divided into : 



The forty-three Bones of the Head : 

 Thirty-two in the Skull, 

 Eleven in the Hyoid Apparatus ; 

 The ninety-three Bones of the Trunk : 

 Fifty-nine in the Vertebral Column, 

 Twenty-six Ribs, 

 Eight in the Sternum. 

 Of the bones of the axial skeleton, seventy-four lie in the median 



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plane of the body, and are single, and bilaterally symmetrical. They 

 are : 



Six Bones of the Skull, 



One Hyoid Bone, 



The fifty-nine Bones of the Vertebral Column, 



The eight Bones of the Sternum. 



The remaining sixty-two bones are arranged in thirty- one pairs, 

 distributed as follows : 



Thirteen pairs in the Skull, 



Five pairs of Hyoid Bones, 



Thirteen pairs of Bibs. 



The Bones of the Head should be considered first naturally, but 

 because of their complexity it is customary to begin the systematic 

 study of the Skeleton with the less complex Bones of the Trunk. 



VERTEBRAL COLUMN. 



The Vertebral Column may be defined as an irregular bony rod on 

 the dorsal aspect of the body, occupying the middle line. Its cephalic 

 end articulates with the skull, and its caudal end terminates in the 

 tip of the tail. It gives rigidity to the trunk, and is joined through 

 the shoulder and pelvic girdles to the Anterior and Posterior Ex- 

 tremities. By uniting with the ribs it completes the dorsal part of the 

 chest or thorax. 



Attached to it are large muscles, which move the head, the trunk, 

 and the extremities, or form the muscular walls of the abdomen. 



