42 
MAMMALIAN ANATOMY 
B. THE SKULL. 
i. Shape and General Proportions. 
In this study compare as many examples of human skulls as are 
available and note the extent of individual variation. Some of 
these should be skulls which have been sawn horizontally through 
the walls of the cranial cavity. Determine each aspect studied 
with great exactness, using as the horizontal plane of reference, the 
plane passing through the lower margin of the orbits and the upper 
margin of the external acoustic meatus. This plane is known as 
the “ Frankfort horizontal.” 
Lateral View. —Distinguish cranial and facial regions; deter¬ 
mine and compare facial angles of different species of mammals 
and different individuals of the same species, noting degree of 
prognathism and human tendency in the direction of orthogna¬ 
thism; note extreme reduction of the jaws in certain individu¬ 
als (cf. variation in this respect shown by Boston bull dogs and 
grayhounds); note effect of orthognathism upon the teeth as 
shown in the reduction of the dental arcade with crowding and 
atrophy of the posterior molars. 
Basal View. —Note the position of the occipital foramen, 
compare with other mammals, and explain the difference. 
Vertical View. —Compare relative amounts of facial and 
cranial regions visible in this view of the skulls of different mam¬ 
mals; note individual and racial variations in the proportions of 
the human skull (“long” and “short” heads). 
Frontal View. —Note direction of axes of orbits; compare 
man with other mammals with regard to extent of field of vision 
and range of binocular vision; note correlation of small size of 
nasal region with large eye and brain development and with 
orthognathism. 
Record the observations made by blocking out, in very light lines, 
outline drawings, natural size, of lateral, basal, vertical, and frontal 
views of the skull, and internal views of the floor and roof of the 
cranial cavity. As the study of the special features is taken up, 
record each of these, with care as to details of relationships, upon 
each view in which it is visible. Finally finish up each drawing 
with the usual clear cut outlines. 
