THE EVIDENCE OF THE SKELETON 



13; 



brain can be clearly seen. In an earlier stage of Ammoccetes the 

 two trabecular horns do not meet, but are separated by connective 

 tissue, which afterwards becomes cartilaginous. 



As far, then, as the topography of this basi-cranial skeleton is 

 concerned, the striking points are — the shape of the trabecular 

 portion, diverging as it does around the infundibulum, and the pre- 

 sence on the parachordal portion of the two large auditory capsules. 



These two points indicate, on the hypothesis that infundibulum 

 and oesophagus are convertible terms, that two supporting structures 

 of a cartilaginous nature must have existed in the ancestor of the 

 vertebrate, the first of which surrounded the oesophagus, and the 

 second was in connection with its auditory apparatus. 



Structure of the Hard Cartilages. 



The structure of this hard cartilage of the trabecular and auditory 

 capsules resembles that of the soft, in so far that it consists of large 



A 



Fig. 57. — A, Cartilage op Trabecule op Ammoccetes, stained with Hema- 

 toxylin and Picric Acid. B, Nests op Cartilage Cells in Entosternite 

 of Hypoctonus, stained with Hematoxylin and Picric Acid. 



cells with a comparatively small amount of intercellular substance. 

 Schaffer, who has described it lately, considers that it is a nearer 

 approach to hyaline cartilage than the soft, but yet cannot be called 

 hyaline cartilage in the usual sense of the term. Its peculiarities 

 and its differences from the soft are especially well seen by its 

 staining reactions. I have myself been particularly struck with 

 the effect of picrocarmine or combined hseniatoxylin and picric acid 



