VASCULAR SYSTEM. 113 



smaller ones. The inner or lining membrane is uniformly 

 thick in all the arteries. 



Q. In what considerable arteries is this fibrous coat thin ? 



A. In the vertebral and internal carotid. 



Q. What, according to Bichat, is the source of cere- 

 bral sanguineous effusion? 



/?. He supposes it always to proceed from the capilla- 

 ries, not from the arterial trunks. 



, Q. What is the organization of this peculiar coat of the 

 arteries? 



#. It is composed of distinct layers of circular fibres. 

 There are no longitudinal fibres. The coat is yellow. 



Q. Is this fibrous coat of the same texture with muscle? 



#. It differs from muscle in its firmness, density, and 

 slight extensibility. The fibrous coat will even break be- 

 fore it will stretch. There is no analogy in their vital 

 properties. 



Q. What then is this arterial coat? 



#. Bichat considers it a distinct texture. 



Q. Why is the arterial structure so strong? 



#. To sustain the impulse of the heart, so that the ar- 

 teries shall not dilate so much as to weaken the onward 

 progress of the blood. 



Q. Does similarity of form alone constitute similarity 

 of texture? 



#. No similarity of properties is likewise necessary. 



Q. How does this differ from the fibrous or peculiar 

 coat of the arteries? 



*#. It is thinner; it is transparent; it has no fibres; it is 

 white. 



Q. What tendency has this coat in old age? 

 15 



