. Text book of zoology. Zoology. Class 2. Pisces. 361 posterior joint of the vertebral column; below this apparently last joint, there is usually a portion supported by rays, and almost congruent with its upper portion, so that the tail appears to be diphyceroal; this is termed a homocercal tail. As a matter of fact, however, it is just like the heterocercal, since the end of the vertebral column is bent upwards, and the dorsal portion of the fin is smaller than the ventral (see Fig. 299 D). In many, actually heterocercal, forms, in which a great length of the vertebral column is bent up, ther
. Text book of zoology. Zoology. Class 2. Pisces. 361 posterior joint of the vertebral column; below this apparently last joint, there is usually a portion supported by rays, and almost congruent with its upper portion, so that the tail appears to be diphyceroal; this is termed a homocercal tail. As a matter of fact, however, it is just like the heterocercal, since the end of the vertebral column is bent upwards, and the dorsal portion of the fin is smaller than the ventral (see Fig. 299 D). In many, actually heterocercal, forms, in which a great length of the vertebral column is bent up, there is an approach to the same structure; since the end of the tail, as regards the exterior, is divided into two almost equal portions : a dorsal, into which the vertebral column is pro- longed, and a ventral, consisting exclusively of rays (Fig. 299 A, B).. Fig-. 299. End of the tail of various Fish: A Sturgeon, B Pike, 0 Salmon, P C o d. h vertebral column, h' bent up termination of the same, ci upper arch, t neural ;spine, n lower arch, n' last lower arch, united with h'. In 0 the bent portion of the vertebral column is still fairly well developed (it is enclosed between the two halves of the caudal fin rays of which the left are removed in the figure), in D, which represents the usual 'Teleostean condition, it is on the contrary very small.—Partly original, partly a copy. In the embryo, and in many cases also, in the newly-hatched animal (Teleostei), the notochord is for some time a straight rod; later the posterior end bends up, and is relatively much larger than in the adult. Well developed, bony, or partly ossified ribs are attached to the transverse processes of the trunk vertebrae in most Ganoids, Teleo- steans, and Dipnoans; in the Selachians the ribs are wanting or very short; they are absent also from the Cyclostomes. There is. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and
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