24 MUSCLES OF THE ABDOMEN 



a. The Cortical Substance forms the external 

 layer. It is of a darker color, and somewhat mottled 

 owing to the presence of the Malpighian bodies. 



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 Malpighian pyrainids. The apices of 

 these pyramids unite to form a ridge lying in the long 

 axis of the kidney. The openings of the uriniferous 

 tubules are found upon this ridge. 



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 \\\& pelvis. The expanded pelvis clasps the 

 ridge described above, receiving thus the excreted 

 urine. The cavity of the pelvis also extends outward 

 for some distance along each pyramid. 



D. THE DIAPHRAGM. 



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 vertebrae by two thick muscular slips or crura. 



b. From the ensiform cartilage. 



c. From the cartilages of the posterior ribs. 



