356 



Comparative Anatomy — Its History, Aim, and Method 



Animals can be compared as wholes with respect to external fea- 

 tures such as color, size, form of body, and appendages. Complete 

 comparison, however, requires that the animal be taken apart and 

 compared part by part. Then the question arises, what parts should 

 be compared? The obvious answer is "corresponding parts." The brain 

 of one animal is to be compared with the brain of the other animal, 

 heart with heart, and so on. Of course, any two things can be compared. 

 If a brain be compared with a liver, some similarities may be found and 

 many marked differences will be found. But the net result has no 

 special significance. It seems obvious that it would be equally futile to 

 compare a breathing organ with a sense-organ. Experience, however, 

 teaches that it is wise to be careful about the obvious. To the ancients 

 the world was obviously flat. As a test case, let us compare a simple 



SPIRACLE 



NASAL PIT 



MOUTH 



FIN 



MEDULLA OBLONGATA 

 SACCULUS 

 RUDIMENTARY GILL 

 SPIRACLE 



QUADRATE CART. 

 MANDIBULAR MUSO 



MANDIBLE 

 BASIHYAL CART 



B 



SPSftSRP* 01 D CORACOMANDI BULAR 



MUSCLE 



MUSCLE 



Fig. 287. Dogfish head. (A) Side view. (B) Cross section at plane indicated by 

 the line C-D in the side view. (Modified from Neal and Rand: "Chordate Anat- 

 omy," Philadelphia, The Blakiston Company.) 



