198 DEVELOPMENT OF THE MARSUPIAL SKULL, 



septum. This is the structure which has been called by Parker 

 the "recurrent cartilage," and by others the " paraseptal carti- 

 lage." As I think there is good reason for believing that 

 Parker's view of its being trabecular in origin is erroneous, the 

 latter term seems preferable. 



Meckel's cartilage is pretty well chond rifled and of large size. 

 Posteriorly it passes into the badly deflned condensation of cells 

 which represents the auditory ossicles. The hyoid is a small, 

 cartilaginous, curved rod which passes inwards to meet the 

 median basihyal. A well defined thyroid can likewise be readily 

 made out, also meeting the basihyal. 



The relationships of many of the structures will be better 

 understood from the actual sections than from the reconstruction; 

 and 1 have, therefore, given figures of a number of the more 

 important with brief descriptions. 



Section A (Plate x.,fig.2). This section is through the anterior 

 nares, and shows the nasal capsule imperfectly chondrified. The 

 two capsules unite at the median septum, but whether the septum 

 is really part of the capsule or an anterior development of the 

 trabeculae, is not apparent from the section. There is some reason 

 to believe that the lower part, at least, of the septum is trabecular. 



Section B(fig.3). Tiiis is a transverse section near the middle 

 of the nasal capsule, and through the front of the opening between 

 the nose and the mouth. As yet the secondary palate, though 

 in large part formed, is widely open, and the tongue lies between 

 the two halves of it. The alinasal cartilage is well developed and 

 slightly chondrified, as is also the septum. By the side of the 

 base of the septum the paraseptals are distinctly seen, but imper- 

 fectly chondrified. Below the lower part of the alinasals are seen 

 the large groups of osteoblasts about to form the maxillce. At 

 this plane is seen also the anterior union of Meckel's cartilages 

 (not shown in the figure). 



Section C(fig.4) is only a short distance behind B, and is figured 

 to show Jacobson's organ. The organ is unusually short, being 

 seen only in eleven sections, and opens directly into the nasal 

 cavity. 



