302 STRUCTURE OF THE VERTEBRATES 



canals and pores in relation to the scales differs widely. In a few 

 fish the cranial canals run through the skull bones. 



Many investigators have attempted to homologize the lateral 

 line organs with other organs of special sense. Patches of lateral 

 line receptors are thought to have migrated into the olfactory 

 pits and mouth, and to have inpocketed to form the ear. How- 

 ever, as the system appears almost completely developed in 

 anuran larvae, and then as completely disappears, including 

 the lateral nerve; and, as the organs appear synchronously in 

 the vertebrates, it seems more logical to the author to assume 

 that these structures developed independently. 



B. Taste Buds 



The taste buds, in their individual structure, more nearly re- 

 semble the lateral line organs than any other sensory organs. 

 The taste bud consists of a cone of supporting cells enclosing 

 an inner cone of taste receptors. The latter lie in a depression 

 in the supporting cells, connected with the outside through a 

 taste pore. The taste buds are found in the oral cavity and 

 pharynx. In the mammals they are most prominent on the 

 tongue, where groups of taste buds are collected on relatively 

 large papillae. 



Taste is one of the chemical senses, the substance with a 

 detectable taste being necessarily in solution. Most ''taste" as 

 recognized by the human is olfactory, taste being limited to 

 elementary sensations of bitter, sweet, sour, salt, etc. As sweet 

 and bitter can be more easily detected in different parts of the 

 mouth, it is reasonable to conclude that there is a specialization 

 of function in the different buds. 



C. Olfactory Sense 



The olfactory sense, like taste, is chemical. The odors detected 

 by water living animals are in solution, and in land living verte- 

 brates the gases become dissolved in the layer of moisture 

 covering the epithelium. The sensory epithelium is located in 

 olfactory pits, the axones of the receptors passing posteriorly 

 to the dendrites of the olfactorv lobe. 



A 



