BRAIN PATTERN 23 



By what means and by what structures is a fish enabled to 

 make use of its surroundings, ^liich must contain such a vast 

 number of different sapid substances ? The organs of taste in 

 man are represented by certain patche^^ or groups of pecuHarly 

 modified cells of the superficial layers of the skin, which are lodged 

 in the thickness of the surface layers of the tongue. These groups 

 of cells have a bud-like arrangement, and have therefore been 

 termed taste-buds. Without going into details at the j^resent 

 stage, it may be stated that they are found on the tongue, the throat, 

 and at the entrance to the windpipe. Leydig discovered in fishes 

 flask-shaped organs, similar to taste-buds, in certain parts of the 

 skin, and they also occur in the mucous membrane of the mouth 

 and throat in those animals. 



We shall describe later certain other sites in which they are 

 found in fish. 



Taste-buds have been compared in general form and appearance 

 to the leaf -buds of a plant, but the arrangement of their cells may 

 be also likened to the segments of an orange. They are flask- 

 shaped bodies, the base of the flask lying in the depths of the skin 

 or mucous membrane, and the neck projecting towards the free 

 surface. The cells are enclosed in a sort of adventitious capsule, 

 but the most superficial cells of this are perforated to allow of 

 access of the apex of the taste-buds to the free surface : the ceUs 

 that form the bud do not actually reach the surface, but from their 

 apices arise fine hairlets which project into an opening called the 

 gustatory pore. By this means the ceUs receive stimuli from the 

 various substances in solution, and from these cells sensory impulses 

 are carried to the centres in the brain. 



The lobes that receive all these impulses are the vagal and 

 facial lobes. The vagal lobes are both sensory and motor in 

 function receiving sensory impulses from the gifls and pharynx, 

 and they have also a motor area known as the nucleus ambiguus 

 from which efferent fibres pass by the vagal motor root : the facial 

 lobes receive sensory fibres from the taste-buds situated on the 

 skin, mouth, lips and barbels, but the facial nerve has also a small 

 motor branch leading to the neck muscles. 



A broad summary of the facts relating to these two lobes can 

 be made in Herrick's words " the vagal lobe for mouth-tastmg and 

 the facial lobe for skin-tasting are local erflargements of the visceral 

 sensory brain. All the taste-buds in the pharynx and back of 

 the mouth are supplied by the vagal and glossopharyngeal nerves, 

 those in front of the mouth the lips, the barbels, and outer skin from 

 the root of the facial nerve." 



