04:4 Dr. F. E. jBcddard on the Bloiv-Jtoles and 



the external orifices of the nasal passages that the right- 

 hand passage ends anteriorly in. a funnel-shaped dilatation, 

 Avhile that of the left side is tubular throughout tliis region, 

 and for the rest of its course is represented merely by the 

 external groove. The large chamber forming the funnel of 

 the right nasal passage gradually narrows into a " stem,'^ and 

 the left-hand nasal passage passes inwards from the external 

 groove, in which it ends externally. The two come close 

 together. It is to be noted that their position within the 

 head is not symmetrical. The right-hand tube occupies as 

 nearly as possible the centre of the cross-diameter of tlie 

 liead, while the left nasal tube is therefore necessarily on the 

 left-hand side. Furthermore_, both tubes lie nearer to the 

 dorsal surface of the head, being at the end of the first 

 one-sixth of the vertical diameter. With them, both above 

 and between, are certain cartilages which will be dealt with 

 later. The two nasal passages are by no means circular in 

 outline. Their exact form differs in different regions. In 

 the first section they are much flattened from above down- 

 wards, and are thus even sht-like. In this region they also 

 lie obliquely to the longitudinal axis of the head, the tilt 

 being upwards on the left side. The two passages are not 

 quite in the same plane, the left being rather dorsal to the 

 right. They are, however, at any rate, roughly of the same 

 length. A little later on, the left nasal passage becomes 

 smaller than the right and alters its angle of position. The 

 right tube maintains its obliquity in reference to the axis of 

 the head, while the left becomes entirely parallel to the 

 horizontal axis. 



Both these changes are accomplished at a distance of 

 some 4'9 mm. from the end of the snout. A little later 

 there is a further change. The left-hand tube groAvs smaller 

 than the right, and its long axis is now bent downwards, as 

 is that of the riglit, and the angle between them gradually 

 diminishes. This state of affairs goes on developing, and at 

 last the two nasal passages lie completely parallel with each 

 other, but with the long axes of both parallel with the 

 vertical axis of the head. At the same time the size of the 

 tubes becomes again equal. All this is accomplished at a 

 further distance of about 3*3 mm. from the last point which 

 was measured. 



As we follow the series of sections away from the blow^- 

 holes, the two nasal passages retain their vertical ])Osition, 

 but, instead of remaining of equal size, the left becomes 



