PRESIDENT'S ADDRESS. xliii. 



fishes, as well as in the whole group of Ganoids, now almost 

 extinct. In the Crocodiles many of the dermal-plates show ossifi- 

 cation, and occasionally among the Mammalia. The armour 

 of the existing Armadilloes, and the extinct gigantic Glyptodon 

 afford a striking example of the co-existence of a well-developed 

 bony envelope, with a complete osseous endo-skeleton. There 

 is a variation in the structure of the vertebrae, even in the different 

 regions of the same animal ; there is one general plan pervading 

 throughout. The centra are disc-like, more or less elongated. 

 The posterior and anterior faces articulate with the next succeed- 

 ing centrum by an intervening cartilage. Each centrum has a 

 channel for the reception of the spinal-column, which is 

 protected by the neural arch, surmounted by the neural spine. 

 The neural-arch is articulated with the anterior one, by which it 

 is strengthened. Towards the extremity the vertebrae are 

 reduced to the centra only, the neural and haemal elements being 

 entirely absent. 



In a description of the skeleton of osseous Fishes it may be 

 as well to remark that the distinction into regions, cervical, 

 dorsal, lumbar, and caudal, so well marked among the 

 vertebrates, is not so in the case of fishes. Owing to the 

 pectoral-vertebra being fixed to the lower base of the skull, and 

 the expansion of the haemal-arches for the protection of the 

 viscoral cavity, there is no neck, or cervical region. The dorsal 

 portion of the vertebral column must be considered as com- 

 mencing with the first vertebra, the pelvic-arch has no bony 

 attachment to the spinal column, there is no sacrum, and no 

 marked separation between the dorsal and caudal elements ; 

 there is consequently no proper lumbar region. In most fishes, 

 especially among the eel-kind, the caudal portion forms a con- 

 siderable part of the whole length of the body. The flexibility 

 of the vertebral-column of fishes affords free movement through 

 the water, and the function of the lateral-fins is only for 

 balancing the body, and not for locomotion. In the conforma- 

 tion of the skull there are several departures from that of the 

 ordinary form in the higher vertebrates, which adapt it for the 



