THE VENTRAI, CAVITY 53 



The cavities are called dorsal and ventral, or neural and 

 visceral. Briefly speaking, they may be described as situated 

 posteriorly and anteriorly to the solid part of the spinal column 

 or bodies of the vertebrae. 



The spinal canal is a part of the dorsal or neural cavity which 

 extends into the interior of the skull, the bones of the cranium being 

 modified vertebrae, and the cavity within them representing the 

 uppermost or cranial part of the neural canal. 



The dorsal or neural cavity contains the brain and spinal cord, 

 well protected within firm, unyielding walls. 



The mouth, neck, thorax, abdomen and pelvis inclose the ventral 

 or visceral cavity, which is in front of the spinal column. The 

 bony walls are very incomplete, especially in the abdomen. They 

 are finished out by muscles; this arrangement allows the walls to 

 be flexible and yielding in character, thus securing to the organs 

 contained that freedom of movement which is necessary to their 

 perfect action. The diaphragm (page 97) divides the ventral 

 cavity into two portions, upper and lower; the pelvic floor (page 

 no) completes the boundary below. 



The ventral cavity contains the organs of respiration, circula- 

 tion, digestion and reproduction; also the kidneys and bladder, 

 which are organs of elimination. 



Having studied the bones of the dorsal and ventral cavities or 

 those of the head and trunk, we will proceed in Chapter IV to 

 those of the extremities. 



