. Chordate morphology. Morphology (Animals); Chordata. glossopharyngeal nerve IX temporal canal facial nerve (VII) root^ spiracle supraorbital canal. infraorbital canal oral canol jugal canal ventral-line organs Figure 13-27. Sensory-line system of Squo/us aconthias. (After Norris and Hughes, 1920) the preopercular division, extends down and forward to be- come the mandibular division on the lower jaw. The ter- minology here is confusing. The mandibular segment of the hyoid arch line anteriorly joins the oral segment of the mandibular arch line. The preopercular division ends be- hind and belo
. Chordate morphology. Morphology (Animals); Chordata. glossopharyngeal nerve IX temporal canal facial nerve (VII) root^ spiracle supraorbital canal. infraorbital canal oral canol jugal canal ventral-line organs Figure 13-27. Sensory-line system of Squo/us aconthias. (After Norris and Hughes, 1920) the preopercular division, extends down and forward to be- come the mandibular division on the lower jaw. The ter- minology here is confusing. The mandibular segment of the hyoid arch line anteriorly joins the oral segment of the mandibular arch line. The preopercular division ends be- hind and below the spiracle without connecting with the temporal portion of the main lateral line. The posterior pit line, single or double, extends toward but not to the mid- line in front of the endolymphatic pores. Some of the lines are open grooves; these include the entire hyoid arch line, the oral portion of the mandibular arch line, the posterior tip of the jugal extension, and the lateral line posterior to the spiracle. The others are closed canals opening to the surface through irregularly spaced pores. There is a pit line from the spiracle down toward the junction of the jugal and oral lines. The significance of this pit line is not known, but it may be the satellite of the post- orbital section of the mandibular arch line. Pit lines such as this are not constant in position nor relationships, while others, as remnants of canals, are more fixed in position. In most selachians, such as the dogfish (Figure 13-27), the canal pattern is suggestive of that observed in CUamydo- seiachus; however, the mouth is far back below a strongly developed rostrum. Development of the rostrum has appar- ently distorted the proportions of the canals. The infraor- bital canal ends below the tip of the snout. (The canals of either side meet and join for a short distance in Laemargus; this fusion occurs well back from the ends of the canals just in front of the mouth.) In Laemargus the supraorbital, inf
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