A TURTLE 133 



Exercise I. Make a drawing of the carapace, showing accurately the 



outlines of the horny plates, and label them. 

 Exercise 2, Make a similar drawing of the plastron. 

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



accurately the outlines of the scales ; label all the organs. 



The Mouth and Pharynx. Open the mouth and disarticulate the 

 lower jaw, after cutting the angle on each side. The mouth and 

 pharynx form a single space ; of this the pharynx is the hinder part, 

 where the course of the air from the nostrils to the lungs crosses 

 that of the food from the mouth to the stomach. Observe the form 

 and arrangement of the plates covering the jaws. Find the internal 

 nares, the inner opening of the nostrils. Observe the floor of the 

 mouth ; note the shape and character of the tongue, and the open- 

 ing of the glottis just behind it, through which air is admitted into 

 the trachea and the lungs. Probe the glottis and note the two ary- 

 tenoid cartilages which guard the opening and form a part of the 

 larynx. Place a blowpipe in the glottis and inflate the lungs. 



Exercise 4. Draw two sketches, one of the floor and one of the roof 

 of the mouth, on a scale of 3. 



The Internal Organs. Open the body cavity in the following 

 manner: Saw or cut through the bridge connecting the carapace 

 and the plastron on each side, taking care not to cut too deeply. 

 Then with the scalpel or scissors cut the skin where it is attached 

 to the plastron, both in front and behind. Placing the animal 

 on its back, 1 carefully raise the plastron at the forward end, and 

 with a scalpel cut the muscles where they are attached to its inner 

 surface. Care must be taken to keep the blade at all times close 

 to the plastron in order to avoid cutting the organs within. Re- 

 move the plastron, first noticing the glistening fibrous periosteum 

 and the muscle attachments on its inner surface. 



Observe the ventral aspect of the animal. A tough membrane, 

 the peritoneum, will be seen covering the body cavity, within which 

 the viscera will be indistinctly visible. The body cavity is divided 

 into two compartments,— the abdominal cavity and the pericardial 



x If a towel is rolled up lengthwise and the roll is made into a ring, a stable 

 support will be obtained to rest the animal upon during the dissection. 



