THE BONES OF THE SKULL. 99 
upper border of the sternum lies on a level with the disc between the second and 
third thoracic vertebre. 
The lower aperture, of large size, is bounded in the middle lne behind by the 
twelfth thoracic vertebra; . 
passing thence the twelfth 
ribs slope outwards, down- 
wards, and forwards. From 
these a line carried horizon- 
tally forwards from their 
tips touches the end of the 
eleventh rib, and then curving 
shehtly upward reaches the 
cartilage of the tenth rib. 
Here it follows the conflu- 
ent margins of the cartilages 
of the tenth, ninth, eighth, 
and seventh ribs, finally 
reaching the xiphoid cartilage, 
where it forms with the costal 
margin of the opposite side 
the subcostal angle, the 
summit of which coincides 
with the xiphi-sternal articula- 
tion; in expiration this joint 
usually lies on a level with 
the intervertebral disc between 
the ninth and tenth thoracic 
vertebre, and corresponds 
with the surface depression 
familiarly known as the pit 
of the stomach. The inferior 
aperture of the thorax is 
occupied by the vault of the 
diaphragm. 
n 
In the foetal condition the 
form of the thorax differs from 
that of the adult. It is laterally 
compressed—in this respect re- 
sembling the simian type. Its Fic. 76.—THE THORAX AS SEEN FROM THE RIGHT SIDE. 
antero-posterior diameter is 
relatively greater than in the adult. At birth changes in form take place dependent on 
the expansion of the lungs; during subsequent growth, the further expansion of the 
thoracic cavity in a transverse direction is correlated with the assumption of the erect 
posture, and the use of the fore-limbs as prehensile organs. 
Sexual Differences.—The thorax of the female is usually described as being 
proportionately shorter and rounder than the male. It also tends to narrowness in the 
lower segment. It is hardly necessary to point out that the natural form is often 
modified by the use of tight or ill-fitting corsets. 
THE BONES OF THE SKULL (Ossa CRANI). 
The term skull (cranium) is commonly employed to signify the entire skeleton 
of the head. This comprises the bony envelope which surrounds the brain 
(cranium cerebrale), and the osseous structures which support the face (cranium 
viscerale, ossa faciel). 
In catalogues of craniological collections the terms used are as follows :— 
Skull | =entire skeleton of head, including the mandible. 
Cranium =the skull, minus the mandible. 
Calvaria =that part of the skull which remains after the bones of the face have 
been removed or destroyed. 
