SUBPHYLUM VERTEBRATA 



321 



gled with the fibers of the periosteum. In some cases striated muscles 

 have ceased to be under the control of the will and thus in a sense 

 have become involuntary. Such are some of the muscles used in swallow- 

 ing. The involuntary, or non-striated, muscles are found mostly in the 

 walls of the alimentary canal and the blood vessels. The cardiac muscles 

 are in the wall of the heart. Both involuntary and cardiac muscles are 

 usually not recognized as part of the muscular system but as parts of the 

 systems to which the organs containing them belong. 



346. Digestive System. — The digestive systems of different verte- 

 brates present many modifications. In general the system may be 



Scopulo 



Acetabulum 

 Femur 



Coracoid ] 



Clavicle 

 Radius 



AyW//?fP Me fa tarsals I ^ 



17 py 'Phalanges ^ocac^C^ 



Fibula 



— <^ Phalanges 



Fig. 214. — Diagram to illustrate the homology between the skeletons of the fore and hind 



limbs. 



divided into an alimentary canal, beginning at the mouth and ending at 

 the anus, and accessory organs, including glands connected to the ali- 

 mentary canal by ducts. The regions of the alimentary canal are, in 

 order, mouth, pharynx, esophagus, stomach, and small and large intes- 

 tines (Fig. 215). 



The mouth cavity, also called the buccal cavity, usually contains jaws 

 bearing teeth for the mastication of the food and a tongue which is used 

 in handling the food and may assist in securing it. In connection with 

 the mouth may be several pairs of salivary glands the secretion of which, 

 the saliva, contains an enzyme, ptyalin. This in an alkaline medium con- 

 verts starches into sugars. The saliva also contains the secretion of 

 mucous glands lying in the walls of the mouth; it serves to moisten the 

 food and make its swallowing easier. 



