GET ACE A. 123 



are small in comparison to many of the Cetacea, and notwith- 

 standing these latter are so immeasurably large, they swim with 

 great rapidity. The air enclosed in their chest, and the enor- 

 mous quantity of fat on their body helps to sustain them in the 

 water surrounding them, and their general form is perfectly fitted 

 for the kind of movements they are called upon to perform. Their 

 long, thick tail is an oar as powerful as that with which nature has 

 endowed the most vigorous and most active fishes, and the fin 

 which terminates it, in place of being vertical, as in the latter, is 

 placed horizontally, a position which is singularly favourable for 

 raising them to the surface when they require to breathe the air. 

 '22. Their anterior extremities, as we have said, are trans- 

 formed into fins : nevertheless, these organs possess the basis of 

 the same structure as the arm of man, the paw of a dog, or the 

 wing of a bat. We find in them the same bones, except that the 

 humerus and bones of the fore arm are shortened, and those of 

 the hand flattened and enveloped in a tendinous membrane, which 

 confines motion almost exclusively to the articulation of the 

 shoulder. Sometimes, the phalanges are more numerous than in 

 other mammals; in other respects these oars only serve the ani- 

 mal in preserving his equilibrium and changing his course ; the 

 tail being his true organ of motion. The posterior extremities 

 are entirely wanting : but we find at the posterior part of the 

 abdomen, two or three rudimentary bones, suspended in the flesh, 

 which are the vestiges of the pelvis. (See First Book of Natural 

 History.) Beneath the caudal vertebrae, there are bones in the 

 .form of the letter V, which afford points of attachment to the 

 flexor muscles of the tail, and increase their strength : it is to be 

 remarked also, that the cervical vertebrae, although seven in num- 

 ber, are very short, and generally, almost entirely soldered 

 together. Finally, the petrous bone, that part of the cranium 

 which encloses the internal ear, in place of being confounded witn 

 other parts of the temporal bone, is separate from the rest of the 

 head, ana adheres to it by ligaments 



23. The senses generally seem to be obtuse in these animals 

 They never have an external ear ; they often want the olfactory 

 nerves; the tongue is almost irnmoveable, and their skin is 

 generally covered with the thickest kind of epidermic layer. They 

 display but little intelligence. Their brain is nevertheless large, 

 and its hemispheres are well developed. 



24. In the Cetacea, the apparatus of respiration possesses pecu- 

 liarities of structure, the utility of which is evident The nares 



22. What is the general conf .rmation of Cetacsa ? 



23. Do the Cetacea possess all the senses in perfection? 



21. What are the peculiant'es of the apparatus of respiration ' 

 11* 



