THE ENDOSKELETON: VERTEBRAL COLUMN AND RIBS 67 



E. VERTEBRAL COLUMN OF TELEOSTS 



i. The tail vertebrae. — Examine a separate dried tail vertebra of any bony 

 fish. Note that the vertebra is very much harder and more opaque than the 

 dogfish vertebrae, owing to the fact that it is composed of bone. Identify the 

 same parts as already seen in the dogfish vertebrae : the biconcave or amphicoe- 

 lous centrum bearing a minute canal in its center for the notochord, the neural 

 arch terminating in a very long sharp neural spine, the haemal arch terminating 

 in a similar haemal spine. The neural canal or space inclosed within the neural 

 arch is generally smaller than the haemal canal inclosed by the haemal arch; in this 

 way the dorsal and ventral sides of the vertebrae may be distinguished. The 

 spines are directed posteriorly. In some fish there are two neural spines to each 

 vertebra, an anterior and a posterior one; the second one probably corresponds 

 to the intercalary arch of the dogfish. Draw a vertebra. 



2. The trunk vertebrae. — Obtain a separate dried trunk vertebra of a bony 

 fish. Identify as before the centrum and the neural arch and neural spine. 

 The haemal arch and spine appear to be missing. Instead there is a pair of 

 projections at the sides of the base of the centrum to each of which a long slender 

 rib is articulated. These stumps or transverse processes are the opened bases of 

 the haemal arch. Draw a vertebra with ribs. 



The centra of teleost vertebrae are arch centra formed by the fusion of the bases of the 

 basidorsals and basiventrals chiefly, although interdorsal and interventral elements may be 

 added to the ends of the centra (Fig. 22B). The neural arch is formed by the basidorsals, 

 the haemal arch by the basiventrals. 



3. Section through the trunk of a bony fish. — In such a section identify 

 the parts already described for a similar cross-section of the dogfish. Note the 

 muscle segments, the centrum and neural arch and spine of the vertebra, and 

 the coelom with its lining. Find the ribs located just outside of the coelomic 

 lining. The ribs are in a different position than those of the dogfish, which are 

 in the horizontal skeletogenous septum. The ribs of teleosts are situated just 

 outside of the coelomic walls. They are false or subperitoneal ribs. Make a 

 diagram of the section, showing the position of the ribs. 



4. Further study of ribs. — Some fishes have two (or more) pairs of ribs 

 simultaneously on each vertebra. Examples are Polypterus, a crossopterygian 

 ganoid from Africa, and many teleosts, including members of the salmon, herring, 

 and pike families. Examine the skeleton of Polypterus and note two pairs of 

 ribs attached to each vertebra. The dorsal pair attached to the transverse 

 processes of the vertebrae are the true or intermuscular ribs; the ventral pair 

 loosely attached to the ventral surface of the centrum are the false or subperito- 

 neal ribs. Vertebrae of fishes like the salmon may also be examined, or sections 

 through the trunks of such fishes. Note the ventral or subperitoneal ribs, and 

 the dorsal or intermuscular ribs (also called epipleurals) located in the horizontal 



