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MESSRS. F. M. BALFOUR AUI) W. N. PARKER OK THE 
outgrowths of the haemal processes, while the wholly independent prolongations of the 
haemal processes appear to be about to give rise to the haemal arches of the tail. 
This peculiar state of things led Gotte, and subsequently one of us, to deny for 
Elasmobranchs all homology between the ribs and any part of the haemal arches of the 
tail; but in view of the explanation just suggested, this denial was perhaps too hasty. 
We are the more inclined to take this view because the researches of Gotte appear 
to show that an occurrence, in many respects analogous, has taken place in some 
Teleostei. 
In Teleostei, Johannes Muller, and following him Gegenbaur, do not admit that 
the haemal arches of the tail are in any part formed by the ribs. Gegenbaur 
('Elements of Comp. Anat.,’ translation, p. 431) says, "In the Teleostei, the costi- 
ferous transverse processes ” (what we have called the haemal processes) <£ gradually 
converge in the caudal region, and form inferior arches, which are not homologous with 
those of Selachii and Ganoidei, although they also form spinous processes.” 
The opposite view, that the haemal arches of the tail in Teleostei contain parts 
serially homologous with the basal parts of the haemal processes as well as with the 
ribs, has been also maintained by many anatomists, e.g., Meckel, Aug. Muller, &c., 
and has recently found a powerful ally in Gotte. 
In many cases, the relations of the parts appear to be fundamentally those found in 
Lepidosteus and Amia, and Gotte has shown by his careful embryological investiga¬ 
tions on Esox and Anguilla, that in these two forms there is practically conclusive 
evidence that the ribs as well as the haemal costiferous processes of Gegenbaur, which 
support them, enter into the formation of the haemal arches of the tail. 
In a great number of Teleostei, e.g., the Salmon and most Cyprinoids, &c., the haemal 
arches in the region of transition from the trunk to the tail have a structure which at 
first sight appears to support Johannes Muller’s and Gegenbaur’s view. The 
haemal processes grow larger and meet each other ventrally ; while the ribs articulated 
to them gradually grow smaller and disappear. 
The Salmon is typical in this respect, and has been carefully studied by Gotte, who 
attempts to show (with, in our opinion, complete success) that the anterior haemal 
arches are really not entirely homologous with the true haemal arches behind, but that 
in the latter, the closure of the arch below is effected by the haemal spine, which is 
serially homologous with a pair of coalesced ribs, while in the anterior haemal arches, 
i.e., those of the trunk, the closure of the arch is effected by a bridge of bone uniting 
the haemal processes. 
The arrangement of the parts just described, as well as the view of Gotte with 
reference to them, will be best understood from the accompanying woodcut (fig. 3), 
copied from Gotte’s memoir. 
Gotte sums up his own results on this point in the following words (p. 138): "It 
follows from this, that the half rings, forming the haemal canal in the Undermost 
trunk vertebrae of the Salmon, are not (with the exception of the last) completely 
