216 



COMPARATIVE PHYSIOLOGY. 



1. To consult a number of plates, such as are usually fur- 

 nished in works on anatomy, in order to ascertain in a general 

 way the relations of the heart to other organs, and to the chest 

 wall, as well as to become familiar with its own structure. 



3. To supplement 

 this with reading the 

 anatomical descrip- 

 tions, without too great 

 attention to details at 

 first, but with the ob- 

 ject of getting his ideas 

 clear so far as they go. 

 3. Then, withplates 

 and descriptions before 

 him, to examine sever- 

 al dead specimens of 

 the heart of the sheep, 

 ox, pig, or other mam- 

 mal, first somewhat 

 generally, then syste- 

 matically, with the 

 purpose of getting a 

 more exact knowledge 

 of the various struct- 

 ures and their anatom- 

 ical as well as physi- 

 ological relations. 



We would not have 

 the student confine his 

 attention to any single 

 form of heart, for each 

 shows some one struct- 

 ure better than the 

 others ; and the addi- 

 tional advantages of 

 comparison are very 

 great. The heart of 

 the ox, from its size, 

 is excellent for the study of valvular action, and the framework 

 with which the muscles, valves, and vessels are connected ; 

 while the heart of the pig (and dog) resemble the human organ 

 more closely than most others that can be obtained. 



Fia. 186.— The left auricle and ventricle opened and 

 part of their walls removed to show their cavities 

 (Allen Thomson). 1, right pulmonary vein cut 

 short; 1', cavity of left auricle; 3, thick wall of 

 left ventricle ; 4, portion of the same with pap- 

 illary muscle attached ; 5, 5', the other papillary 

 muscles; 6, one segment of themitral valve; 7, 

 in aorta is placed over the semilunar valves. 



