26 PHYSIOLOGY AT THE FARM. 



origin namely, the posterior aorta, the larger, and the 

 anterior aorta, the smaller division, 



Jugular Veins. The right and left jugular veins, which 

 receive the blood from the several veins about the mouth, 

 begin by a communication with the venous system of the 

 brain at the jugular foramen between the petrous portion of 

 the temporal bone and the occipital bone, and finally unite with 

 the axillary vein, coming on each side from the anterior ex- 

 tremity, to form the anterior vena cava, and that conveys the 

 blood into the right auricle of the heart. 



Nerves. While the blood serves for the maintenance and 

 repair of living parts, the nerves are concerned in the sensibil- 

 ity and the movements of the same. When a bit of marble is 

 taken into the mouth it makes an impression on the extremities 

 of the nerves touched, and these convey the impression to the 

 brain the effect of which is a state of consciousness referred 

 to the parts with which the marble is in contact. This con- 

 stitutes a sensation. Again, when a bit of sugar is taken into 

 the mouth, it melts and affects the nerves of the tongue ; the 

 impression here also is conveyed by these nerves to the brain, 

 the effect of which is also a state of consciousness, referred, as 

 before, to the place over which the melted sugar has become 

 diffused. This is also a sensation ; but if the animal had pre- 

 viously been conscious of the peculiar sensation afforded by 

 sugar, it might recognise the sensation as something which 

 had before occurred in its consciousness. This recognition 

 seems to be what constitutes perception. If a dog has been 

 often treated to a bit of sugar, it will get up and run in haste 

 when it sees the door of the cupboard opened where the sugar 

 is kept, in expectation of getting a bit at the moment. Here, 

 then, the remembrance of the sensation prompts to action. 

 The action consists in muscular movement, and that move- 

 ment is determined by nerves acting through the brain on the 



