THE CRANIAL NERVES AND LATERAL SENSE ORGANS OF FISHES. 127 



canal at the pre-opei'culum, the eleventh helow and the twelfth ahove the ridge of bone 

 just mentioned. 



It is thus seen that the hyomandibuiai- canal is perfectly independent of any of the 

 others, and does not anastomose either with the infra-orbital or lateral canals. 



(4) Lateralis Canal. 

 First or Supra-temporal Portion. 



As with the infra-orl)ital canal, it will bo most convenient to describe the lateral canal 

 under the headings of its various supjiorting ossicles. 



First Supra-temporal or Extra Scapula.— The supra-temporal canal commences b lin dly 

 in both G. morj^hua and G. vij'ens at the anterior extremity of the first supra-temporal 

 ossicle. Its direction is markedly inwards and forwards. The greatest length of the 

 ossicle is 17 mm., and its greatest breadth 6 mm. It is free anteriorly, that is, it has no 

 articulation with any otlier bone, but its extremity is attached by a ligament to the 

 dorsal spiny process of the parietal overhanging the foramen transmitting the so-called 

 " cutaneous branch of the Vth." * Posteriorly the ossicle articulates by means of an 

 oblique convexity with tlie second supra-temporal. The first supra-temporal consists of 

 an internal plate, having its dorsal edge turned over somewhat considerably to protect 

 the supra-temporal canal. Anteriorly the portion turned over tapers down to admit of 

 the entrance into the canal of the first or proximal dermal tubule. 



Second Supra-temporal or Extra-scapula. — Supports the distal or basal portion of the 

 supra-temporal canal, and consists of an internal plate, the two edges of which have more 

 or less become opposed to form a tube. Posteriorly this apposition is complete, so that the 

 tube is here perfect, thougii the two edges in question have not fused, such not being a 

 characteristic of the Cod. Anteriorly, however, the tube, as in most of the other lateral 

 line ossicles, is imperfect, but this is to enable the second dermal tubule to eater the 

 canal. The upper posterior border of the ossicle bears a semicircular notch, which fits 

 into the upper or epiotic limb of the post-temporal. The internal face of the second 

 supra-temporal also rests on this limb of the post-temporal. The greatest length of the 

 second supra-temporal is 17 mm., and its greatest width about 11 mm. Anteriorly it 

 presents a concave border for articulating with the first supra-temjooral, whilst posteriorly 

 it articulates with two ossicles : a, by a long, slightly convex, ventral facet with the 

 third supra-temporal ; b, by a backwaixlly directed posterior facet (slightly concave) with 

 the fourth supi"a-temporal. Posteriorly the supra-temporal portion of the lateralis canal 

 takes a dowuAvard curve and becomes confluent with the latei-al or body portion. 



Second or Lateral Portion. 



The first 20 mm. of this section of the lateral cjinal are supported partly by the third 

 supra-temporal, biit also partly by the ventral jiortion of the second (see PI. 21. fig. 1). 

 This fact must be taken into consideration when reading the description of the former 

 ossicle. 



* =the R. lateralis acoessorius (sec Section N, p. 16G). 



