JYasal Passaofs of the CacJtdJot. G49 



It may be fnrtlior pointed out tliat at tlie bcj^inning of 

 tlie cartilage covering tlie riglit nasal tube — wliere it is wide, 

 completely separated here from the groove on the surface of 

 the head, and lying in a direction at right angles to the 

 vertical axis of the head — the cartilage considerably overlaps 

 the nasal tube; it extends beyond it towards tlie latei-al 

 surface of the head, but also slightly upwards for a distance 

 of perhaps half the length of the tube itself. Later on what 

 has been the dorsal surface of the nasal tube becomes its 

 outer lateral side, and ultimately there are other changes, 

 as we have already described in considering the course of 

 the nasal tubes. In fact, what is originally the dorsal 

 surface of the nasal tube becomes ultimately — after the two 

 tubes are fused to become the nasal pharynx — the ventral 

 surface, owing to the gradual twist, already described, in 

 the course of the tube. We cannot therefore insist vipon 

 an exact comparison between the cartilages associated w^ith 

 it and those associated with the very different nasal passages 

 of Phoccena referred to above. 



On the left side this narrow cartilage ultimately fuses 

 with the median piece, but I could not detect a similar 

 fusion on the right side. It is finally overwhelmed by the 

 growth of a second outgrowth of the median cartilage, which 

 I take to be the ali-ethmoid. The anterior cartilages are 

 presumably to be regarded as the ali-nasals ^. The fusion 

 of ali-nasals and ali-ethmoids is accomplished at a distance of 

 about 9 mm. from the extremity of the head. There is no 

 connection between the median internasal septum and the 

 upgrowth of the basal portion of the ethmoid until a point 

 at about 6 mm. from the anterior end of the head. And, 

 moreover, this point is quite easy to detect. The median 

 nasal cartilage, lying between the two blow-holes, up to a 

 point about 6 mm. from the anterior end of the snout, is 

 perfectly symmetrical. But the incompletely or wholly 

 unchondrified tissue surrounding it bends to the right at 

 its end. In the next section this is seen to contain a 

 cartilaginous rod which is the median dorsal growth of the 

 ethmoid, and thus would seem to have fused with the 

 median nasal cartilage rather than to have arisen as an 

 outgrowth from it. It will be noted also that from this 

 point the median septum of the head acquires a symmetrical 

 position and is no longer on the left side as in the anterior 



*■ See, e. //.,W. K. Parker, ''On the Structure aud Development of tlie 

 Skull in the MamuDalia. Part II. Edentata; Part III. lusectivora," 

 Pbil. Trans. Piov. Soc. 1885. 



