NECTURUS 65 



The Appendages. The two pairs of legs are nearly of the same 

 size and are widely separated from each other. Each leg is com- 

 posed of three divisions,— a proximal, a middle, and a distal divi- 

 sion. In the fore limb these segments are the upper arm, the 

 forearm, and the wrist and hand respectively; in the hind limb 

 they are the thigh, the shank, and the ankle and foot. 



Note the position of the limbs with reference to the trunk, which 

 in Necturus is of a primitive character. In their most primitive 

 position the limbs of vertebrates are straight and extend at right 

 angles to the body. Each limb has in this position a dorsal and a 

 ventral surface, and an anterior, or preaxial, and a posterior, or 

 postaxial, surface. If the human arm is extended straight out 

 from the body with the thumb up, it will assume this primitive 

 position ; the back of the hand will be dorsal, the palm ventral, and 

 the thumb preaxial, or anterior, in position. 



The first modification of this primitive position, which occurred 

 as a result of locomotion on a hard surface, was the bending of the 

 middle segment of the leg ventrally and the distal segment more or 

 less dorsally. The proximal segment retained its primitive posi- 

 tion ; the middle segment bent downward ; and the distal segment 

 assumed more or less its original position again, at right angles to 

 the body but in a different plane. This is approximately the posi- 

 tion the limbs have in Necturus ; it enables the limbs to raise the 

 trunk above the ground and to propel it slowly forward. 



Exercise 1. Draw the dorsal aspect of the animal. 



Exercise 2. Draw the ventral aspect. 



Exercise 3. Draw a side view of the head on a scale of 2 or 3, showing 

 accurately the gills, eyes, nostrils, and lips. 



The animal may be killed by immersing it in warm water (about 

 43 C, or no° F.) or by putting it under a bell jar with a wad of 

 cotton soaked in chloroform or ether. While under the influence 

 of the anaesthetic a large quantity of slime usually exudes from its 

 skin ; this slime must be scraped off. 



The Mouth and Pharynx. Cut back through the angle of the 

 jaw on each side until the lower jaw can be laid back and the 

 mouth and pharynx fully exposed. 



