171 
orbital canal has 3 pores and 4 sense organs, the left supra- 
orbital 3 pores and 2 sense organs, and the supraorbital 
commissure one median pore and a pair of sense organs. 
Only the two extremities of the left supraorbital canal are 
present, the whole of the intermediate portion having 
aborted with the corresponding part of the left frontal. 
The first two pores and first sense organ of the left supra- 
orbital appear to correspond to the same on the right. 
The whole supraorbital system is supplied by the two RR. 
ophthalmici superficiales vii. 
Besides the sense organs situated in the sensory 
canals, or canal organs, there are two other series of naked 
sense organs situated on the skin. These are known as 
Pit Organs and Terminal Buds. The former belong to 
the lateral line system, and are innervated by one or more 
of the four lateral line nerves. The latter are quite dis- 
tinct from the lateral line organs, and are innervated by 
an entirely separate system of nerves, the Ramus lateralis 
accessorius (= R. lateralis trigemini), belonging to the 
communis system. The terminal bud system has been 
reduced in the Plaice. 
2.—TneE Nose (Fig. 25).* 
The olfactory organ of both sides is described as if 
viewed from above, and not from the side. The external 
apertures of the nose, two on each side, are not symmetri- 
cally placed, and those of the left side are situated almost 
on the apparent mid-dorsal line of the body, immediately 
to the left of the anterior border of the left eye. The 
two apertures or nostrils of each side are sometimes called 
anterior and posterior nares, but the latter term is 
obviously inadmissible. 
* For the olfactory organs of the Pleuronectide, see Kyle, Jour. Linn. 
Soc., xxvii., and 18th Ann. Rep. Fish. Board Scotland, 1899, Part iii. 
