organ systems of different vertebrates, and compare them with 

 corresponding organ systems of the frog. 



B. THE SKELETON. 



In connection with the dried prepared skeleton, study the fresh 

 skeleton, boiled for a few minutes after removing the skin and 

 viscera. 



I. GENERAL ARRANGEMENT OF PARTS OF THE SKELETON. 



a. The main axis consists of the vertebral column continued 

 anteriorly as the central part (brain case) of the skull. 



b. Connected with the main axis are the supporting parts of 

 the appendages, and the lateral parts of the skull. 



1. The anterior appendages consist of a free limb (containing 

 a hiimcrus, radio-ulna, carpus and digits, supported by a shoulder 

 girdle or pectoral arch. 



2. The posterior appendages consist of a free limb (containing 

 a femur, tlbio- fibula, tarsus and digits) connected with the spinal 

 column by the pelvic girdle. 



II. VERTEBRAL COLUMN. 



f 



Made up of nine separate vertebrae and of a posterior Urostyle. 



a. Remove the third vertebra, and note : 



1. Solid flattened ventral part (centrum), with anterior concave, 

 and posterior convex surfaces. 



2. Neural arch ; arising dorsally from the centrum and enclosing 

 a space which forms with that of the other vertebrae, the neural 

 canal. 



3. Processes of the vertebrae; on each side, one transverse 

 process, four articular processes, one on each side of arch anteri- 

 orly (pre-zygapophysis) , one on each side of arch posteriorly (post- 

 sygapophysis) , a median spiuous process arising from dorsal sur- 

 face of the arch. 



b. The first vertebra (atlas), articulates anteriorly by two 

 surfaces with the skull. 



The eighth vertebra (sacrum} has a large transverse process join- 

 ing the pelvic arch and a centrum convex anteriorly and with two 

 tubercles posteriorly to articulate with the- 



c. Urostyle, a single rod-like bone continued posteriorly as a 

 cartilage and with a dorsal ridge anteriorly, inside which is a small 

 neural canal opening laterally by two small foramina, one on each 

 side. 



Draw the third vertebra to show the points mentioned 



63 



