Anatomy of Notovyctes typhlops. 85 



thinning out greatly, as also the cartilage underlying tlie ventral 

 nasal furrow, so that, about the level of the exit of Stensoii's 

 duct from the nasal furrow, there is no cartilage left in this 

 region, except for remnants of the outer nasal floor cartilage 

 (Fig. 4, n.f.c), and the outer bar of Jacobson's cartilage {o./.b.). 

 Thus, hei-e the median and lower lateral parts of the cartilaginous 

 crescent disappear first as compared with the Rabbit,^ and, 

 contrasted with the Guinea-pig,-^ the upper lateral or lower 

 lateral parts of which go tirst. At first this remnant of cartilage 

 appears to become directly connected by its perichondrium with 

 the lower edge of the crescentic bone (Fig. 5) as found by Klein in 

 the Guinea-pig ; soon the cartilage disappears altogether, leaving 

 a very thin bony shelf (Fig. b, p.p.s.) in its place. Compare this 

 with Perameles,^ and also with the Macropodidae* in so far that 

 the cartilages of Jacobson form an incomplete tube, becoming 

 reduced posteriorly. At this level, nerve fibres occupy almost 

 the whole space between the bone and the mesial wall of the 

 Organ. 



Posterior to the Organ of Jacobson the inferior septal ridge 

 still remains because of the persistence of the bony shelf, which 

 anteriorly helped to support Jacobson's Organ ; while, as far for- 

 ward as the anterior end of the Organ, the primary lateral ridge 

 {p.l.r.), which has been for a short distance devoid of .special 

 support, is invaded by a thin lamina of bone from the maxillary 

 bone, becoming the maxillo-turbinal {m.t.). In the hinder part 

 of this region the palatal processes are overlain in the middle 

 line by the anterior portion of the vomer, so that there is now a 

 complete bony partition between the right and left nasal cavities, 

 from dorsal to ventral or palatal surfaces. 



Ducts of Jacobson and of Stenson. 



The duct connecting the lumen of Jacobson's Organ with the 

 nasal cavity (Fig. ?>,J.d.) is very short, .06 mm.., since the wall 

 enclosing the ventral sulcus of the extreme anterior end of the 

 Organ lies almost immediately in contact with the mesial edge, 



1 Klein: Q.J.M.S., vol. xxi., p. 554. 



2 Loc. cit., pi. vii., flg. 2. 



3 Proc. Linn. Soc. N.S.W., vol. xi., n.s., 1896, p. 600, fig. 8. 



4 Jour. Anat. and Phjs., vol. 26, p. 372. 



