FORM OF THE ARTERIES. 221 



Form of the Arteries. 



Bichat and Richerand have considered every arterial tube 

 to be evenly cylindrical, the diameter of it only being 

 diminished when branches were sent off. Beclard believed 

 that they had the form of a truncated cone, with the base 

 turned towards the heart, some of them, as the carotids for 

 example, being enlarged at the place of division. Others be- 

 lieve with Professor Homer,* " that the arterial system in its 

 general configuration may be compared to a tree, the trunk of 

 which is attached to the heart, and which, by a continued suc- 

 cession of divisions and subdivisions reaches to every part of 

 the body. There are no means of estimating rigidly the collec- 

 tive area of the branches in proportion to that of the trunk ; 

 but a little observation on the size of the primitive branches, 

 will satisfy one of a great excess* on the part of the latter, and 

 as the rule is maintained throughout, there must finally be an 

 immense disproportion. We have then reason to believe, that 

 if all the branches were assembled into a single cavity, this 

 cavity would be somewhat like a cone, the apex of which 

 would be next the heart. The same rule holds in regard to 

 the venous system, it being observed, however, that the latter 

 has two trunks connected with the heart instead of one. The 

 general rule is therefore established throughout the vascular 

 system, that the collective area of the branches is always 

 greater than that of the trunk from which they proceed. By 

 the same rule the circulation in the branches must be more 

 languid than in the parent trunks, as this circulation is retarded 

 both by additional friction, and by having to fill up a larger 

 canal."* 



Nevertheless, Professor Horner, gives a computation made 

 by Mr. Erskine Hazard from actual measurement of the arte- 

 ries, from which it appears, that in many of them at least, the 

 area of the large trunks before subdivision is greater than that 

 of their divided branches united, and consequently that the 



* A Treatise on General and Special Anatomy, vol. ii. p. 155, by W. E. 

 Horner, Prof, of Anat. University Penn., &c. &c. j fourth edition. 



19* 



