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 Alalpighian 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 JMalpighian pyramids. 



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 pelvis. The expanded pelvis breaks up 

 into a number of smaller divisions, calices, each of 

 which clasps the apex of a pyramid. With a little dis- 

 section this arrangement of the pelvis may be demon- 

 strated. 



n. 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 vertebree by two thick muscular slips or 

 crura. 



b. From the ensiform cartilage. 



c. From the cartilages of the posterior ribs. 



