THE SENSES. 197 



Lymphatics of the upper extremities. The superficial set accom- 

 pany the superficial veins, and pass through two or three glands 

 situated at the inner condyle ; having joined the deep lymphatics 

 which accompany the venae comites, they proceed onwards to the 

 axilla, and pass through the axillary glands ; following , the course 

 of the axillary vein, they pass beneath the clavicle, join the lym- 

 phatics of the neck, and terminate in the thoracic duct. The 

 lymphatics of the right upper extremity, and right side of the neck, 

 unite to form the right or lesser thoracic duct, which opens into the 

 right vena innominata. 



The lymphatics of the trunk consist of a deep and superficial set ; 

 in the chest, the former are seated between the muscles and pleura, 

 in the abdomen, between the muscles and peritoneum, the super- 

 ficial being subcutaneous. The viscera contained in the chest and 

 abdomen also have a superficial and deep layer of lymphatics the 

 deep being distributed through the peculiar tissue of each organ, 

 the superficial running beneath the membranous envelope. 



Lymphatics have been denied to the brain and spinal cord, and 

 to the ear, eye, and placenta. For a beautiful view of lymphatics, 

 see steel plate, Frontispiece. 



CHAPTER XIV. 



THE SENSES. 



THE senses are the means by which the mind becomes acquainted 

 with external objects. Without the materials which they furnish, 

 its exercise would be impossible. When the mind has once ex- 

 perienced various sensations, the memory can recal them when they 

 are gone ; the judgment can compare them, and can perceive their 

 relations, and the imagination can combine them into endless 

 varieties ; but still, with all this, we are incapable of figuring to 

 ourselves any image, the elements at least of which have not first 

 been made known to us through sensation. 



The senses generally enumerated are five, viz. touch, taste, 

 smell, hearing, and vision. There are other sensations,, however, 

 such as those of thirst, hunger, nausea, sneezing, &c., which cannot 

 properly be classed under any of these heads. 



