The Latero-Sensory Canals and Related Bones in Fishes. 417 



As the preopercular canal passes from the preoperculum into the 

 mandible, it is paralleled by a second, and smaller tube formed by 

 the anastomosis of two branches of the two adjoining dendritic systems. 



According to Wright [82\ there is in Lepidosteus, as *in Amia, 

 a latero-sensory organ in the dorsal end of a diverticulum of the 

 spiracular canal, innervated by a branch of the ramus oticus. No 

 mention whatever of this organ is made by Collinge, and it is not 

 shown in my reconstruction. This latter fact however is not of great 

 importance, for the reconstruction was evidently intended to simply 

 show the canals. 



According to Wright "there is a well-marked groove on the roof 

 of the otic cartilage, which with Sagemehl may be called the 'temporal' 

 groove"; but this groove must differ markedly from that in Amia, in 

 that it is apparently limited to the otic region, does not open on to 

 the posterior surface of the skull, and lodges no anterior extension 

 of the trunk muscles. This is evident from Parker's sections of 

 larvae [56', pi. 36, fig. 1 — 6]. 



The general arrangement of the latero-sensory canals of Lepido- 

 steus is thus seen to differ from that of Amia in certain minor details 

 only. But comparison with elasmobranchs and with the chondrostean 

 ganoids show that these minor details are not unimportant, and that they, 

 in reality, indicate transitional conditions between those fishes and the 

 teleosts. This will be further discussed under the heading Elasmobranchii. 



Crossopterygidae. 



Polypterus Mchir. In Polypterus [6] the supraorbital canal first 

 runs forward through the os terminale, and at the anterior end of 

 that bone anastomoses, by its second primary tube, with the second 

 primary tube of the main infraorbital line. It then turns sharply 

 backward and traverses the two nasals and the frontal, and on leaving 

 the latter bone anastomoses, by its terminal primary tube, with that 

 primary tube of the main infraorbital canal that is given off as the latter 

 canal passes from the postfrontal into the squamosal. The os terminale 

 and the two nasals each lodge a single sense organ, and they are 

 apparently together equivalent to the single nasal bone of Amia. 



Internationale Monatsschrift für Anat. u. Phys. XXI. 27 



