THE EVIDENCE OF THE SKELETON 133 
brain can be clearly seen. In an earlier stage of Ammocates 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 cesophagus 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 trabeculee and auditory 
capsules resembles that of the soft, in so far that it consists of large 
Fic. 57.—A, CarTILaAGE OF TRABECULH OF AMMOC@TES, STAINED WITH Hama- 
TOXYLIN AND Picric Acip. B, Nests of CartinaGk CELLs In ENTOSTERNITE 
OF HYPOcTONUS, STAINED WITH H@mMATOXYLIN 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 hematoxylin and picric acid 
