44 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL. i. 



Do the ribs pass backward and form a part of the lower arches 

 -of the tail ? In case it should be demonstrated that ribs chondrify 

 independently of the transverse processes, there are no ribs in the 

 tail of Amia. Otherwise it may be a question of definition. While 

 there is a suture separating the bone of the lower arch from the 

 vertebral centrum in the tail, there is no segmentation of the carti- 

 lage. The lateral halves of the most anterior six or seven arches 

 unite below the great blood vessels to form the haemal canal, and 

 immediately below the point of union there is a joint followed by a 

 long spine. This spine might possibly be regarded as being a pair of 

 fused ribs. 



The ribs and the transverse processes pass outward immediately 

 beneath the peritoneum, as do those of most, but not all, Teleostomi. 

 Anteriorly the transverse processes rise high up on the sides of the noto- 

 -chord ; but, as already stated, I have nowhere found them coalescing 

 with the bases of the upper arches. Scheele has found the bases of 

 the lower arches in the most anterior vertebras of Rhodeus to spring 

 from a common mass of cartilage with the bases of the upper arches. 

 Proceeding from this fact he concludes that the Cyprinidae are a more 

 primitive form than the Salmonidse, in which upper and lower arches 

 .arise independently of each other; and that the ribs of Teleosts are 

 homologous with those of Amphibians. In the latter conclusion he 

 wholly ignores the fact, first demonstrated by Aug. Miiller and later 

 emphasized by Rabl (50), Hatschek, and Baur (12), that the ribs of 

 these two groups of animals occupy very different positions with ref- 

 erence to the lateral muscles, and the further fact that some fishes 

 possess both kinds of ribs. As to the Cyprinidae, it has appeared to 

 me that they are in many respects much more highly differentiated 

 fishes than the Salmonidae. This is shown in the universal absence 

 of teeth on the bones of the mouth, the great modification of the 

 lower pharyngeal bones and the development of teeth on them, the 

 modification of the anterior vertebrae to the service of hearing, and 

 the enormous reduction of the cartilage found in the vertebral col- 

 umn of the lower fishes. Moreover, instead of the Cyprinidae being 

 more ancient than the Salmonidae, they appeared, so far as our knowl- 

 edge goes, at a considerably later period, the beginning of the Mio- 

 cene ; the Salmonidae near the beginning of the Cretaceous. 



Hence, we have every reason for concluding that the condition 

 of the upper and the lower arches and the cartilages connected with 

 them is in a more primitive stage in the Salmonidae than in the Cyp- 

 Tinidae. We have now the testimony of Amia to the same effect. Upper 

 .and lower arches arise almost universally independently of each 



