54 VERTEBRATE ZOOLOGY 



skeleton in preparation, they must be carefully preserved. It is of 

 great practical use to have a dried skeleton at hand for comparison 

 during the dissection. It is not necessary that this skeleton be 

 thoroughly cleaned and mounted : any skeleton that has been dried 

 after the muscles have been removed and the bones laid bare 

 will answer the purpose. 



The Axial Skeleton; the Vertebral Column and the Ribs. The 

 vertebral column consists of a succession of bony vertebrae closely 

 connected by intervertebral ligaments. They are deeply biconcave, 

 or amphicoelous ; the two concavities are joined by a central canal, 

 and all these spaces are filled with the jellylike notochord. The 

 notochord thus forms a continuous structure which runs the length 

 of the vertebral column. 



The vertebral column may be divided into two regions: the 

 trunk region, in which ribs are present ; and the caudal region, 

 in which they are absent. Each trunk vertebra is composed of a 

 biconcave body, or centrum, from the dorsal side of which arises 

 the neural arch, and from the ventrolateral side of which projects 

 a pair of long haemal processes. The neural arch is composed of a 

 pair of neural processes and a long median neural spine ; it incloses 

 the spinal cord. Projecting from the lower part of the ante- 

 rior edges of the neural processes is a pair of small articular 

 processes called the prezygapophyses ; they articulate with a pair 

 of projections from the posterior end of the centrum of the 

 next vertebra, called the postzygapophyses. 



The ribs are long, slender bones which project from the haemal 

 processes. The first four or five vertebrae have no haemal processes, 

 and the ribs project from their centra. The ribs of teleosts are not 

 homologous to those of the higher vertebrates but represent the 

 distal ends of the haemal processes. Extending from the ribs is also 

 a series of long, slender bones which lie in the myocommas and 

 may be homologous to the ribs of the higher vertebrates ; they are 

 called intermuscular bones. 



The caudal vertebrae differ from the others in that the haemal 

 processes meet in the midventral plane and fuse, forming a haemal 

 spine and inclosing a space— the haemal canal— in which lie the 

 caudal vein and artery ; they also do not bear ribs. 



