172 COMPARISONS OF STRUCTURE IN ANLMALS. 



of those fin-limbs, and indeed with every other 

 part of their organization, being, in fact, what 

 ' it ought to be in animals so expressly formed 

 for the medium they tenant, and the part 

 assigned them in creation. 



Let us take one of the fishes with a truly 

 osseous skeleton, say tlie *perch, and investigate 

 the details of the spine. From the head to 

 the caudal fin, a column of vertebral bones is 

 carried nearly in a straight line, or in a line 

 more or less arched; and to these bones and 

 their mode of articulation, the vigorous actions 

 and the flexibility of the tail are owing. In 

 the mammalia, the vertebree are divided into 

 cervical, dorsal, lumbar, and so on ; but in 

 fishes, no such division is admissible. Fishes 

 have no true neck, and no chest ; they breathe 

 by means of gills on each side of the head at 

 its junction -with the body, and are conse- 

 quently destitute of those voluminous lungs, 

 which, with the heart, are contained in the 

 chest of quadrupeds. Yet, there is a division 

 in the vertebrce of fishes, for the more anterior 

 are furnished with ribs,* varying in develop- 

 ment ; in the perch they are rather slender, 



* In some fishes, the ribs are mere rudiments, and in others, 

 as the skate, they are wanting. 



