48 COMPARATIVE ANATOMY. 



SAGEMEHL, M. Bcitragc zur Anat. der Fische. Morphol. Jahrb. IX., 1884. 



WIEDERSHEIM, R. Salamandrina perspicillata. Versuch. einarvergl. Anatomic der 

 Salamandrinen. Genua, 1875. (Annali del Miweo civico. Vol. VII.) Die 

 Anatomie der Gymnophionen. Jena, 1879. Das Skelet und Nervensystcm von 

 Le,pidosiren annectens. Morphol. Studien, Heft I. Jena, 1880. 



II. RIBS. 



The ribs, standing in the closest connection with the myocom- 

 mata (rayotomes) of the great lateral muscles of the body, are 

 arranged segmentally, and onto- as well as phylogenetically, pass 

 through a membranous, a cartilaginous, and a bony stage. Their 

 development, which as a rule takes place first in the anterior part 

 of the body and then extends gradually backwards, is usually 

 entirely independent of the vertebral column, their connection with 

 it being a secondary one. 1 



Fishes and Dipnoi. The cartilaginous or bony ribs are 

 attached to the basal processes already described, and extend 

 ventro-laterally from the corresponding vertebrae. The 

 ribs of Fishes show a very primitive condition, usually extending 

 along the whole length of the vertebral column (Lophobranchii, 

 Spatularia). In rare cases they are absent, though many Fishes 

 only possess rudimentary ribs (many bony Fishes, Elasmobranchs). 



In others, as in numerous Teleosteans and Ganoids, they are 

 very well developed, and encircle the body-cavity like the hoops of 

 a cask ; but they never unite together in the mid-ventral line. 



The relations of the anterior portion of the vertebral column to the auditory 

 organ in certain Teleosteans will be described later (see p. 207). 



Amphibia. In the ribs of Amphibia there are evident 

 signs of degeneration ; as a rule they are confined to the region of 

 the trunk, or at most they extend in certain Urodeles in a very 

 rudimentary form as far as the first two caudal vertebrae ; in other 

 cases, as in the tailless Batrachia, they are so remarkably short 

 that they can no longer be said to encircle the body-cavity. In 

 many Anura the ribs are not distinctly articulated, as they become 

 fused with the broad transverse processes (Fig. 32, E). 



The ribs of Urodeles are forked at their proximal ends, and articulate with 

 the bifurcated transverse processes of the vertebrae. The ventral limb only <>f 

 the transverse process corresponds to the basal process of Ganoids ; the dorsal 

 one is to be looked upon as a neomorph. The bifurcated ends of the ribs in 

 Reptiles and Birds as well as the double articular facets of the ribs of Mammals 

 are to be explained in the same manner. 



1 The ribs of Ganoids, and possibly also those of Dipnoi, seem to follow an 

 entirely different plan of development, in that they become segmented off from the 

 lower arches, as mentioned in the chapter on the vertebral column. 



