GUIDES FOR VERTEBRATE DISSECTION 



EXTERNAL FEATURES 



How many regions head, neck, trunk, tail, etc. can you 

 distinguish? Do you find any indications of scales on or in the 

 skin? Do you find any median or paired fins? Are any of them 

 supported by fin-rays? Is the tail diphy-, homo-, or heterocer- 

 cal? * Where is the anus? 



Examine the head for nostrils, eyes, ears, mouth, etc., noting 

 the position of each. Is the mouth wide or narrow? Terminal 

 or inferior in position? Are lips present? Are there any eye- 

 lids? Probe with a bristle through the nostril (external nans) 

 and note the position of the opening (choana or internal nans) 

 where it enters the mouth. 



How many external gills do you find? Look between them 

 for gill-slits (visceral or branchial clefts); how many on each 

 side? How many pairs of legs occur? Can you find in each 

 the same regions thigh, upper arm, shank, forearm, ankle, 

 wrist, etc. as occur in your limbs? How many toes in each 

 foot? Note the peculiar way in which the limbs stand out at 

 nearly right angles to the body. Make out in each a dorsal and 

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

 postaxial, side. 



In the trunk region notice the impression of the muscle- 

 plates upon the skin. How many plates can be counted between 

 fore and hind limbs? 



Draw a side view of the animal, natural size, labelling the 

 parts. 



INTERNAL STRUCTURE 



I. MUSCULAR SYSTEM 



REMOVE the skin from the head and trunk by cutting down 

 the middle line of the back and then skinning laterally until the 

 whole is free. Take great care not to injure the underlying 

 muscles. The external gills need not be removed with the skin. 



* Diphyccrcal, tail alike above and In-low, the parts symmetrically 

 arranged around the vertebral column; horaocercal, the upper and lower 

 lobes of the tail alike, the vertebral column extending into the upper lobe; 

 heterocercal, the lobes unequal, the vertebral column extending into the 

 upper lobe. 



