THE AUMY IIOKSE. 23 



the top of the skull. In this position it separates the ncek 

 muscles of the right side from those of the left. The object 

 of elasticity in this ligament is to permit of great freedom in 

 the motion of the head, although supporting its great weight 

 in proper position. 



MUSCLES AND TEXDOXS. 



(Plate IV.) 



The muscles are divided into voluntary and involuntary mus- 

 cles; the former being under the direct control of the will, as, 

 for example, the muscles of the neck, legs, tail, etc. ; and the 

 latter acting independently of the animaPs will, as, for ex- 

 ample, the heart, intestinal muscles, etc. 



The muscles form about one-half of the entire weight of the 

 bod)\ With regard to their form they are divided into long, 

 wide, and short. Long muscles are generally found in the 

 limbs; wide muscles are stretched beneath the skin or around 

 the great cavities of the trunk, and short muscles are found 

 chiefly around the irregularly shaped bones. 



Tendons are white, round or flattened cords affixed to the 

 extremities of long muscles, attaching them to other structures, 

 but themselves neither stretching nor contracting. 



All leg muscles are long muscles. Extensors are those that 

 have the power of straightening the limb; -flexors, of bending 

 the limb. 



The extensor ijedis is the principal extensor of the fore leg; 

 it originates at the lower extremity of the humerus, and its 

 fleshy portion continues to the lower third of the radius; at 

 this point it becomes tendinous, and, passing down over the 

 knee, continues along the front of the leg and becomes attached 

 to the upper and front part of the os pedis. Action, to extend 

 the leg. 



The extensor su-ffraginis has its origin from the external 

 head and outer border of the radius and from the side of the 

 ulna; it is inserted (attached) to the upper and front part of 

 the OS suffraginis. Action, to extend the foot. 



The extensor metacarjyi magnus has its origin from the lower 

 and external surface of the humerus, passes down the front of 

 the radius and kneejoint, and is attached to the upper end of 

 the, large metacarpal l)one. Action, to extend the metacarpus. 



The flexor hrachii has its origin from the lower end of the 



