4 GUIDES FOR VERTEBRATE DISSECTION 



The skeleton consists of axial and appendicular parts; the 

 axial embracing the skull and the vertebral column, the appen- 

 .dicular including the supports of the fins and of the structures 

 (girdles) which unite these to the trunk. 



Study a bit of the vertebral column taken from the tail (caudal 

 vertebrae). Note the elements (vertebrae) of which it is com- 

 posed. There is an axis composed of separate bodies (centra), and 

 dorsal and ventral to this are two arches, flattened from side to 

 side, a neural arch above and a haemal arch beneath. More 

 careful study will show that these arches are composed of several 

 parts. Continuous with each centrum is a neural and a haemal 

 process on either side, and between the successive neural processes 

 a neural or intercalary plate. (In the young the top of each 

 neural process is a distinct and additional neural plate. In 

 specimens not thoroughly cleaned the neural spines will be found . 

 to be connected by an interspinous ligament. Notice the notches 

 or openings (foramina) in processes and plates for the passage of 

 spinal nerves. Should you judge that dorsal and ventral nerve- 

 roots passed through the same or through different foramina? 

 The arches are completed above by small bodies, the neural spines. 

 Are these equal to the centra in number? Do you find analogous 

 haemal plates and haemal spines in the haemal arch? 



Draw several vertebrae, X3, from the side. Also cut and 

 draw two transverse sections of the column, one between two 

 centra, the other in the middle of a centrum, naming the parts. 



Study a few vertebra? from the middle of the trunk (dorsal 

 vertebrae), making out centra, neural arches, and the components 

 as before. Are the neural spines arranged as in the tail? Pro- 

 jecting laterally from each side of each centrum is a transverse 

 process. Could you compare this with a hsmal plate ? 

 Attached to the tip of each transverse process is a short rib. 



Draw several dorsal vertebra, X3. 



Split a bit of this part of the vertebral column in the sagittal 

 plane, and study the cut surface. See that each centrum is 

 concave at each end (amphiccelous), and that the concavities 

 are filled with a gelatinous substance (intervertebral expansions of 

 the notochord). Do the cavities of the two ends of a centrum 

 connect? Make out on the inner surface of the neural arch the 

 parts already seen from the side. 



Draw the section, X3. 



