USE OF CHARTS IN TEACHING VERTEBRATE PALEONTOLOGY 49 
through loss chiefly, of a pre-existing, more generalized type, 
a fact strikingly presented by the discarded parts that accompany 
every ^^finished^^ skull. 
Not least of the advantages of the guide charts was the manner 
in which they assisted the student to become familiar with the 
technical terms. After he has worked out several types and 
labeled each element, every name comes to have a rather definite 
meaning. 
Encouraged with the results gained from the use of the chart 
I for the skull and at the suggestion of the late Dr. S. W. Willis- 
ton, the writer attempted the compilation of guide charts for 
the limbs and the vertebrae. These guide charts, together with 
some suggestions as to their use are presented herewith. 
THE SKULL 
The chart for the skull, plate IX, consists of dorsal, ventral, 
and posterior views. It is accompanied by a form suitable for 
student use in the laboratory. While the chart was designed 
primarily to illustrate the amphibians and reptiles, it may be 
used for the mammals and birds. The solid lines mark the out- 
lines of the skull and, the openings commonly present such as 
the orbits and nares. It is only in exceptional cases, for in- 
stance, to close the otic notch, that these lines should be modified. 
In the dorsal view the elements found in the primitive skull 
are outlined by dots. Each bone in the type to be represented 
should be designated by following its dotted outlines with heavy, 
preferably red, lines. When an element or elements are missing, 
the outlines are ignored and the adjacent bones are expanded 
in the proper directions to fill the space and maintain the proper 
relations. In the exclusion of the lacrimal from the nares 
and in other rare instances, the dotted lines will necessarily be 
changed slightly. 
In the ventral view the same plan is followed as in the dorsal. 
The dotted lines give a choice between a single and a double 
occipital condyle. A large and small interpterygoid vacuity 
are designated by dashed outlines and a dotted line from the 
