CHORDATES IN GENERAL 159 



Divisions of Skeleton of Terrestrial Vertebrate 



I. Axial Skeleton 



(a) Skull 



1. Cranium 



2. Sense capsules 



3. Jaw apparatus 

 (Visceral arches) 



(b) Vertebral column 



1. Cervical vertebrae (neck) 



2. Thoracic vertebrae (chest) 



3. Lumbar vertebrae (small of back) 



4. Sacral vertebrae (hip) 



5. Caudal vertebrae (tail) 



(c) Thoracic basket 



1. Eibs (paired) 



2. Sternum (breastbone) 



II. Appendicular Skeleton (girdles and limbs) 



(a) Pectoral (anterior) 



1. Girdle : scapula, clavicle, procoracoid and coracoid 



2. Limb: Humerus (upper arm), radius and ulna (forearm), carpals 

 (wrist), metacarpals (palm), phalanges (bones of digits) 



(b) Pelvic (posterior) 



1. Girdle: ilium, pubis, and ischium 



2. Limb: Femur (thigh), patella (knee cap), tibia and fibula (shank), 

 tarsals (ankle), metatarsals (sole), phalanges (bones of toes) 



The muscular system represents a system of cells highly special- 

 ized in contractility. Voluntary muscles are usually connected with 

 the skeleton; those of the visceral organs, e.g., intestine, are invol- 

 untary. Cardiac muscle is the highly specialized involuntary muscle 

 which makes up the wall of the heart. 



The digestive system is typically a straight tube extending through 

 the length of the trunk of primitive vertebrates. In the higher 

 forms there are many outgroAvths, such as digestive glands and 

 respiratory organs. The anterior region of the digestive tube is the 

 mouth cavity which contains teeth on the jaws, a tongue, and re- 

 ceives saliva from salivary glands. Following the mouth is the 

 pharynx or throat region. Next comes the esophagus which is usu- 

 ally tubular and propels the ''swallows" of food posteriorly by 

 consecutive waves of contraction, a process known as peristalsis. 

 It leads to the saclike stomach, whose walls possess gastric glands for 

 secretion of a digestive fluid containing enzymes (ferments) and weak 

 hydrochloric acid. The peristaltic contractions continue along the 



