200 VERTEBRATES 



What provision do they have for articulation on the ventral 

 side? On the dorsal? Twist the first vertebra on the 

 second. Do you find the " axis " ? Is it attached to the 

 first or the second vertebra? 



II. Organs of the Thoracic and Abdominal Cavities. 

 (i) Open the skin along the viid-ventral line extending 

 from the breast bone to the pelvic arch. Sever the skin for- 

 ward to the neck and remove the skin from the entire body. 

 Notice the blood supply to the skin in the region of the 

 fore limbs, and also in the region of the hind limbs. Is 

 the skin attached loosely or closely to the body? After 

 removing the skin, note its softness. Would it make good 

 fur? Why? 



(2) Study the distribution of blood vessels in the su- 

 perficial muscles of the body on both dorsal and ventral 

 sides. Make note of any peculiar or prominent vessels. 



(3) Look for indications of bilateral symmetry on dor- 

 sal and ventral sides. If it is a female, count the mammary 

 glands on either side and note their location. Study the 

 muscles of the body as now exposed. Name as many as 

 you can from your knowledge of the muscles of the frog. 

 Do you find any which are not present in the frog? (See 

 page 165.) 



(4) With a sharp scalpel open the abdominal wall from 

 the breast bone to the pelvic arch. Look for the lining 

 of the cavity. What is its nature? What is it called? 

 Note the general position of the abdominal viscera and 

 their method of folding. Do they seem to be segmented? 

 Of what use can that constricted form of intestine be? 



(5) Sever the ribs by cutting the cartilaginous attach- 

 ment along the side of the sternum. Pull them slightly 



