22 NERVOUS SYSTEM OF VERTEBRATES. 



arise the ramus palatinus to the mucosa of the roof of the mouth 

 and a ramus hyoideus which is joined for some distance with the 

 mandibular ramus of the lateral line nerves in the common ramus 

 hyomandibularis, and eventually supplies the hyoid muscles and 

 the mucosa of the floor of the mouth. The ramus hyoideus is a 

 posttrematic ramus, since it runs behind the spiracular cleft when 

 that is present, and there is often a pretrematic ramus running 

 in front of the cleft and arising in common with the ramus palatinus. 



The distribution of the organs of the sense of taste innervated 

 by the X, IX and VII nerves is of great importance. In fish-like 

 vertebrates the taste buds are found in the mouth and branchial 

 cavities. They are also distributed more or less widely on the 

 outside of the head and in extreme cases, as in some bony fishes, 

 on the fins and over almost the entire body. They have usually 

 no regular arrangement in rows and differ from the lateral line 

 organs in that they usually project above the surface and are 

 never depressed in pits or canals. In terrestrial forms the taste 

 organs are confined to the mouth ^vity. 



From the cephalic end of the somatic sensory column of the 

 myelencephalon the fifth cranial or trigeminus nerve takes its 

 origin by a more dorsal sensory and a more ventral motor root. 

 The roots enter a ganglion which is partly divided into two portions, 

 a dorso-cephalic and a ventro-caudal portion. From the dorso- 

 cephalic ganglion a large nerve runs forward through the dorsal 

 part of the orbit and supplies the skin of the snout and dorsal 

 surface of the head. This is the nervus ophthalmicus projundus 

 and its ganglion may be known as the profundus ganglion. The 

 ventro-caudal ganglion is properly known as the trigeminal gang- 

 lion. From it arise two large rami: the ramus maxillaris which 

 supplies the skin beneath the eye and the lining of the front part 

 of the roof of the mouth; and the ramus mandibularis which 

 supplies the skin over the lower jaw and the muscles which move 

 the lower jaw. These two rami are apparently comparable to 

 the pretrematic and posttrematic rami of the branchial nerves, 

 the mouth taking the place of a branchial cleft. The nerve 

 complex consisting of the ophthalmicus profundus and trigem- 

 inus proper is fairly constant in its relations and size throughout 



