276 GENERAL ANATOMY. 



sent an origin, a trunk, branches, twigs, and ramusculi, be- 

 coming smaller and smaller until they reach their termina- 

 tion. 



Each of the arterial trunks arises from a ventricle of the heart, 

 and does not present here a continuation of the substance of 

 the heart, as has even recently been advanced, but an intimate 

 and very remarkable' connexion of the middle membrane of 

 the artery is divided into three festoons, bordered with liga- 

 mentous tissue, the orifice of the ventricle is furnished with a 

 ring of the same tissue, the extremity of the festoons of the 

 artery is firmly fixed to the orifice of the ventricle, and the 

 triangular intervals of the dentations are likewise occupied by 

 ligamentous membranes; the internal membrane of the vessel 

 is continuous with that of the heart, and the external mem- 

 brane is united to the substance of that organ. 



The trunks, the branches and all the divisions of the arteries 

 are obviously cylindrical. There are nevertheless exceptions; 

 some arteries enlarge as they advance, while others seem to 

 contract. The arterial cylinders gradually diminish from the 

 trunks even to the last ramifications. 



Generally the sum of the calibre of the branches is greater 

 than their main trunk, but to this there are exceptions; thus 

 it is not evident, that the carotid and brachial arteries have 

 together a greater capacity than the trunk of the innominata; 

 neither is it certain, that the radial and cubital arteries united, 

 have a greater capacity than the brachial. We must not con- 

 found, in this comparison, the external diameter with the ca- 

 pacity. Besides it very often happens, that the capacity of 

 the arterial branches changes, without an appreciable change 

 in their size; and to cite only an obvious example of it, the 

 uterine arteries augment considerably during pregnancy, while 

 the hypogastric artery which furnishes them, increases but 

 little, and the primitive iliac artery not in an appreciable 

 manner. 



The variable number of the successive divisions of the arte- 

 ries, their mode of division, and the angles which are found 

 between the branches and the trunks, have been indicated 

 [354, &c.] as well as the anastomoses and the lateral passages 



