80 VERTEBRATE ZOOLOGY 



dian tendon into two parts. Split this muscle in the median line 

 and remove the left half so that the muscles beneath will be ex- 

 posed. Two muscles will be seen, the geniohyoid and the cerato- 

 hyoid. The former is a narrow muscle with longitudinal fibers, 

 which extends from the tip of the lower jaw to the hyoid cartilage ; 

 the latter is a thick muscle with an oblique direction, which passes 

 from the hyoid cartilage to the first gill arch. 



In the region of the fore limbs will be seen the pectorals, a pair 

 of fan-shaped muscles whose fibers radiate from the forward side 

 of the arm to the midventral line ; they draw the arms backward. 

 The opposing muscles, which draw the arms forward, are the 

 slender procoraco-humeralis muscles. These will be seen extend- 

 ing directly forward from the base of the arm to the procoracoid 

 cartilages. 



Note in this region the coracoid and the procoracoid cartilages, 

 which are portions of the pectoral girdle ; they are very thin plates 

 which underlie the muscles just mentioned. 



On the upper arm note the two muscles which appear on its 

 ventral surface. The anterior muscle is the flexor, and the pos- 

 terior one is the extensor, of the forearm and hand. On the fore- 

 arm note that but a single muscle is present on the ventral side ; 

 this is the flexor of the hand. In the higher vertebrates this muscle 

 is divided into a number which flex the fingers separately. 



In the region of the hind legs are the femoral muscles, a pair 

 of fan-shaped muscles which extend from the base of the legs 

 to the median line. Extending from the posterior border of these 

 muscles to the anus are the pyriform muscles. 



Exercise 17. Draw the ventral aspect of the animal, showing these 

 muscles. 



The Skeletal System. This system is composed of two distinct 

 portions, the exoskeleton and the endoskeleton. The former is 

 but very slightly developed in Necturus, as in most amphibians. 

 Bony or horny scales or other hardened integumentary structures 

 are not present, the outer surface of the body being protected only 

 by the secretions of the slime glands. Claws are also absent. The 

 only exoskeletal structures present are the teeth and certain bones 



