On the Anatomy and Phylogenetic Position of Polypterus. 403 



lachii and must be coosidered once to have been continuous with the 

 skull wall along its whole extent. The sensory (mucous canal) nerves 

 in Selachii pass through the orbital ledge forming a row of foramina. 

 In Polfjpterus the corresponding branches of the ophthalmicus super- 

 ficialis pass up in the space between the band and the skull wall. In 

 the anterior and posterior regions they still pass through the thin 

 cartilage. The posterior foramen in the figure is that of the Ramus 

 oticus of VAN WijHE. The anterior is one of the many unnamed 

 branches. 



With regard to the passage of the ophthalmicus superficialis from 

 the orbit to its destination the relation is so close between Polypterus 

 and the Notidanidae that the same description will almost serve for 

 both. "Mit dem Austritte durch den Canalis praeorbitalis oder das 

 Foramen praeorbitale gelangt der Nervenstamm auf die Oberfläche des 

 Craniums , wo er bei manchen in eine Rinne eingebettet wird. Diese 

 besteht bei den Notidaniden. Am Ende der Rinne beginnt bei den- 

 selben ein zweiter Canal, der einen Theil des Nerven aufnimmt und 

 seitlich um die Naseukapsel herum nach aussen und unten leitet, so 

 dass dieser Nervenzweig an der lateralen Unterfläche zur weitern Ver- 

 breitung seinen Austritt erhält. Diesen Canal will ich als Ethmoidal- 

 Canal unterscheiden. Der nicht in ihm eintretende Theil des Nerven 

 nimmt medianwärts seinen Weg und verläuft gegen das Rostrum" 

 (Gegenbaur, Unters. Heft 2, p. 70). 



The ethmoidal regions appear at first to show great differences 

 but it may yet be demonstrated that the condition in Polypterus may 

 be derived from that of Chlamydoselachus and the Notidanidae. In 

 the latter types the prefrontal pit (Praefrontal-Liicke) is large and 

 the nasal capsules are wide apart while the bridge of cartilage be- 

 tween is flat and thin. 



Hexanchus and Chlamydoselachus are in this region more primi- 

 tive than Heptanchus. In Ileptanchus the thickened rim (gewulsteter 

 Rand) of the prefrontal pit cuts off a portion of the latter forming 

 a bridge in front of it. This portion forms what may be called the 

 pineal opening for just beneath it (Cattie) lies the anterior end of 

 the epiphysis. In Polypterus the two rims of the prefrontal pit must be 

 considered as having united simultaneously with the raising of the 

 nasal septum which is thin in the middle but massive dorsally and 

 ventrally. Growth forwards of the rim gives rise to the small horn 

 in front of the nasal opening and the ledge above the mucous canal 

 in the dermethmoid. 



