830 REPORT OF COMMISSIOJMEE OF FISH AND FISHERIES. [84] 



gions, the body and the tail. They are distiuguished from each other 

 by the characters of the inferior processes of the vertebrae, while the 

 upper arches are connected with the vertebrae in the same manner 

 throughout; and are generally distinguished by the possession of 

 median (spinous) processes. In the region of the trunk, the lower 

 arches are divided into ribs, and supporting transverse processes (par- 

 apophyses). In the tail of the Selachii and Ganoidei they are continu- 

 ously connected with the centrum, and run out into spinous processes, 

 just like the upper arches." (Gegenbaue, Elem. Comp. Anat., p 430.) 

 Again, among fishes, generally the vertebrge of the tail develop infe- 

 rior arches through which the caudal vessels pass. The segments of 

 the column beyond these support ribs which arch over the viscera, but 

 never meet with any sternum mesially, on the ventral parietes. The 

 fins ha?e a skeleton of osseous rays which are supported upon the iu- 

 terhsemal spines. 



So well known are they that it is not my intention in the present 

 connection to enter upon the study of the scales of Amia. It is suf- 

 ficient to say that they are of the cycloid type of structure and consti- 

 tute the exoskeleton of this fish, being arranged much as we find them 

 in the typical Teleosteans. 



Anatomists have long understood the morphology of the skeletal 

 parts of the tails of fishes. Professor Huxley tersely presents the con- 

 ditions for us in these words, when he says that "In all Teleostean 

 fishes the extremity of the spinal column bends up, and a far greater 

 number of the caudal fin-rays lie below than above it. These fishes 

 are, therefore, strictly speaking, heterocercal. Nevertheless, in the 

 great majority of them (as has been already mentioned, page 19), the tail 

 seems, upon a superficial view, to be symmetrical, the spinal column 

 appearing to terminate in the center of a wedge-shaped hypural bone, 

 to the free edges of which the caudal fin-rays are attached, so as to 

 form an upper and a lower lobe, which are equal, or subequal. This 

 characteristically Teleostean structure of the tail-fin has been termed 

 homocercal — a name which may be retained, though it originated in a 

 misconception of the relation of this structure to the heterocercal con- 

 dition." 



"In no Teleostean fish is the bent-up termination of the notochord 

 replaced by vertebrae. Sometimes, as in the* salmon, it becomes en- 

 sheathed in cartilage, and persists throughout life. But, more usually, 

 its sheath becomes calcified, and the urostyle thus formed coalesces with 

 the dorsal edge of the upper part of the wedge-shaped hypural bone, 

 formed by the anchylosis of a series of ossicles, which are developed in 

 connection with the ventral face of the sheath of the notochord." (Anat. 

 of Vert. Animals, page 131.) 



There are ninety vertebrae in the spinal column of Amia calva; they 

 are of the amphiccelous type, and devoid of zygapophysial processes 

 (Fig. 14). The centra of these vertebrae are thoroughly ossified, but their 



