24. MUSCLES OF THE ABDOMEN 
a, lHE, CorRTICAL SUBSTANCE forms the external 
layer. It is of a darker color, and somewhat mottled 
owing to the presence of the Malpeghizan bodces.. 
b.- THE MEDULLARY SUBSTANCE forms the internal 
layer. It is of a lighter color, and striated owing to 
the peculiar arrangement of the uriniferous tubules and 
blood-vessels. The uriniferous tubules are united into 
a number of groups, each of a pyramidal form, and 
known as the AZalpighian pyrameds. 
c. THE Sinus. The medullary substance encloses a 
cavity, the sinus, which is a continuation inward of 
the hilus. It is filled with connective tissue, blood- 
vessels, and the greatly expanded ureter, which here is 
known as the fe/vzs. The expanded pelvis breaks up 
into a number of smaller divisions, calzces, each of 
which clasps the apex of a pyramid. With a little dis- 
section this arrangement of the pelvis may be demon- ° 
strated. 
D: THE DIAPARAGAN, 
The diaphragm is the muscular septum between the 
abdomen and the thorax, and can now be examined 
from the abdominal side. It is a dome-shaped parti- 
tion, partly muscular, partly membranous. 
1. The Central Tendon lies at the top of the dome. 
_ It is a thin membrane passing into muscular substance 
at all points of its circumference. 
2. The Muscular Substance has three origins: 
a. Posteriorly from the bodies of several of the 
lumbar vertebrzee by two thick muscular slips or 
crura. 
b. From the ensiform cartilage. 
c. From the cartilages of the posterior ribs. 
