128 ANATOMY FOR NURSES [Chap. VIII 



(1) . Serous membranes proper. 



(2) The lining membrane of the vascular system. 



(3) The liniiiij inc'nii)rane of certain cavities. 



(1) Serous membranes proper. — With one exception, these 

 membranes form closed sacs, one part of which is attached to the 

 walls of the cavity which it lines, — the parietal portion, — whilst 

 the other is reflected over the surface of the organ or organs con- 

 tained in the cavity, and is named the visceral portion of the mem- 

 brane. In this way the viscera are not contained within the sac, 

 but are really placed outside of it, and some of the organs may 

 receive a complete, while others receive only a partial, or scanty, 

 investment. 



This class of serous membranes includes : — 



(a) The two pleurw, which cover the lungs and line the chest. 



(6) The pericardium, which covers the heart, and lines the outer 

 jfibrous pericardium. 



(c) The peritoneum,^ which lines the abdominal cavity, clothes 

 its contained viscera, and also the upper surface of some of the 

 pelvic viscera. 



(2) The lining membrane of the vascular system. — This applies 

 to the internal coat of the heart, blood-vessels, and Ij-mphatics. 

 It bears a close resemblance to the proper serous membranes in 

 structure and appearance. 



(3) The lining membrane of certain cavities : — 



(a) One illustration of this is the capsule of Tenon. This 

 capsule is a shut sac placed back of the eyeball, with a visceral 

 layer upon the globe of the eye, and the parietal layer next to the 

 bed of fat on which the eyeball rests. 



(6) The brain and spinal cord enclose cavities which are lined with 

 a delicate serous membrane. One of the membranes that envelop 

 the brain and spinal cord (arachnoid) is also a serous membrane. 



Function of serous membranes. — The most important function 

 of serous membrane is protection, which is accomplished in two 

 ways : (1) by forming a smooth, slippery lining or covering for the 

 viscera, blood-vessels, and cavities with which it is associated, and 



1 The peritoneum in the female is the one exception to the rule that serous mem- 

 branes are perfectly closed sacs, as it has two openings by which the Fallopian 

 (uterine) tubes communicate with its ca\nty. 



