2 GUIDES FOR VERTEBRATE DISSECTION 



dicular skeleton of the supports of the limbs and the girdles which 

 connect these to the body. The sternum, usually regarded as a 

 part of the axial skeleton, is, in the case of the frog, best treated 

 in connection with the shoulder-girdle. 



The vertebral column is composed of separate bones, the 

 vertebrae, plus an elongated bone, the urostyle or coccyx, at the 

 posterior end. How many vertebrae do you find? 



Study a single vertebra from about the middle of the column. 

 In it make out a centrum or body from which arises dorsally on 

 either side a neural arch terminating above in a neural spine. 

 Is the centrum procoelous (hollow in front), opisthoccelous (hollow 

 behind), or amphiccelous (concave both in front and behind)? 

 Notice that each vertebra bears a pair of lateral projections, the 

 transverse processes (diapophyses). Do they arise from the cen- 

 trum or from the neural arch? Examine the distal end of each; 

 see the hollow in which, in life, the end of a short rib was inserted. 

 On the anterior and posterior ends of the neural arch notice the 

 articular facets (zygapophyses) by which the vertebrae are con- 

 nected together. Does the postzygapophysis face upwards or 

 downwards? What is the condition in the prezygapophysis? 



Draw dorsal, lateral, and end views of this vertebra, X4, 

 naming the parts. 



Compare other vertebrae with the one studied. How does the 

 first (the atlas) differ from those behind? Does it have both 

 pre- and postzygapophyses? Notice the anterior prolongation 

 of its centrum. Draw this vertebra. Examine the ninth verte- 

 bra (sacrum). Is it procoelous? What is the character of the 

 centrum behind? With what parts does the pelvis articulate? 



Draw three or four vertebrae together, viewed from the side, 

 showing the way in which the zygapophyses overlap and the 

 openings (intervertebral foramina), between the neural arches of 

 the successive vertebrse, for the passage of the spinal nerves. 

 Is there an intervertebral foramen between the first vertebra and 

 the skull? 



Behind the sacrum the vertebral column is continued by 

 the coccyx or urostyle, which must be regarded as composed of 

 coalesced caudal vertebrae. Notice the articular facets by which 

 it is connected with the sacrum, and above them the neural 

 arch. Does this arch continue the length of the bone? Is there 

 an intervertebral foramen between the sacrum and the urostyle? 



