Ii6 ALUS. [Vol. XVIII. 



The ventral ribs lie wholly in the lining membranes of the inner 

 surface of the body wall, opposite the mesial edges of the asso- 

 ciated intermuscular septa ; the rib that is associated with the 

 third vertebra lying opposite the sixth septum. The horizontal 

 ribs lie in the intermuscular septa at the points where those septa 

 cross the horizontal muscle septum, the first or most anterior rib 

 lying in the fourth septum. 



Associated with each of the ventral ribs there is a triangular 

 ligament which lies in and fills the obtuse angle formed between 

 the anterior edge of the basal portion of the rib and a horizontal 

 line on the adjoining anterior part of the lateral surface ot the ver- 

 tebra. The ligament is horizontal in position, lies ventral to the 

 horizontal rib, and extends to the anterior edge of its vertebra. 

 Associated .with the horizontal rib there is a similar but smaller 

 ligament, lying vertically instead of horizontally, and extending 

 from the dorsal surface of the rib, near its base, to the lower por- 

 tion of the spine-like part of the dorsal arch of the vertebra. 



In Scomber there is no slightest external trace, either on the 

 vertebrae or on the ventral surface of the occipital part of the 

 skull, of the ventral cartilaginous processes found in Aiiiia. 



The first two horizontal ribs, in Scomber, seem to be, as will be 

 later shown, the serial homologues of the occipito-supraclavicular 

 ligament of the fish. In Amia the corresponding ligaments seemed 

 to be the serial homologues of the single ribs of that fish. If 

 therefore the first two ribs of Scomber, which have the vertebral 

 articular relations of ventral ones, are the serial homologues of the 

 horizontal ribs of the fish, as their position indicates, the hori- 

 zontal ribs of Scomber, and not the ventral ones, may be the homo- 

 logues of the single ribs of Amia. Neither the horizontal nor the 

 ventral ribs were examined in section, and one or the other of 

 them may be simply "Fleischgraten." The position of the hori- 

 zontal ribs seems to indicate, conclusively, that they are 

 the homologues of the " Seitengraten " of Aloiiacaiithiis, and 

 hence, according to Goette and Goeppert (No. 30, p. 162), the 

 homologues of the upper ribs of the Crossopterygii and Selachii. 

 If they be such. Scomber closely resembles Polypteriis and Cala- 

 moichthys excepting only in the total absence, on the vertebrae 

 examined, of associated supporting basal processes. And if the 



