ON THE MOTION OF THE BLOOD. 61 



the veins; but in adult and advanced age especially, 

 of a texture far more solid and compact, very elastic 

 and strong. 



88. The arteries consist of three coats:* 



I. The exterior, called, by Haller, the tunica cellu- 

 losa propria ; by others, the nervous, cartilaginous, ten- 

 dinous, &c. It is composed of condensed cellular 

 membrane, externally more lax, internally more and 

 more compact: blood vessels are seen creeping upon 

 it:f it gives tone and elasticity to the arteries. 



II. The middle coat consists of transverse fibres, % 

 lunated or falciform, and almost of a fleshy nature: 

 hence this has the name of muscular coat, and ap- 

 pears to be the chief seat of the vital powers of the 

 arteries. 



III. The inner coat lining the cavity of the arteries 

 is highly polished and smooth. This is much more dis- 

 tinct in the trunks and larger branches than in the 

 smaller vessels. 



89. Every artery originates either from the pulmo- 

 nary artery (the vena arteriosa »of the ancients), which 

 proceeds from the anterior ventricle of the heart and 

 goes to the lungs ; or from the aorta, which proceeds 

 from the posterior ventricle and is distributed through- 

 out the rest of the system. These trunks divide into 

 branches, and these again into twigs. 



90. According to the commonly received opinion, 



* For the various opinions respecting the number and differences of the 

 arterial coats, consult among others Vine. Malacarnc, Delia Osscrvat. in 

 Chirurgia. Turin. T. ii. p. 103. 



f Fr. Ruysch, Hespons. ad ep. problematicatn. iii. Also his Tftesaur. 

 Annt. iv. tab. 3. 



X B. S. Albinus, Annot. Academ. L. iv. tab, "u fig. 1. 



