ON THE ARTERIES. 275 



divides into two slips, which are inserted one on each side into the bases 

 of the first phalanges of the toes, leaving an interval between them for the 

 passage of the flexor tendons. The point of division of this fascia into 

 fasciculi and slips, is strengthened by transverse bands, which preserve 

 the solidity of the fascia at its broadest part. The intervals between the 

 toes give passage to the digital arteries and nerves, and to the lumbricales 

 muscles. 



The lateral portions are thin, and cover the sides of the sole of the foot ; 

 they are continuous behind with the internal and external annular liga- 

 ments ; on the inner side with the middle portion, and externally with the 

 dorsal fascia. 



Besides constituting a strong layer of investment and defence to the soft 

 parts situated in the sole of the foot, these three portions of fascia send 

 processes inwards, which form sheaths for the different muscles. A strong 

 septum is given off from each side of the middle portion of the plantar 

 fascia, which is attached to the tarsal bones, and divides the muscles into 

 three groups, a middle and two lateral; and transverse septa are stretched 

 between these to separate the layers. The superficial layer of muscles 

 derive a part of their origin from the plantar fascia. 



CHAPTER VI. ' 



ON THE ARTERIES. 



THE arteries are the cylindrical tubes which convey the blood from the 

 ventricles of the heart to every part of the body. They are dense in struc- 

 ture, and preserve for the most part the cylindrical form when emptied of 

 their blood, which is their condition after death : hence they were con- 

 sidered by the ancients as the vessels for the transmission of the vital 

 spirits,* and were therefore named arteries (aty T^sTv, to contain air). 



The artery proceeding from the left ventrical of the heart contains the 

 pure or arterial blood, which is distributed throughout the entire system, 

 and constitutes, with its returning veins, the greater or systemic circula- 

 tion. That which emanates from the right ventricle, conveys the impure 

 blood to the lungs; and, with its corresponding veins, establishes the 

 lesser or pulmonary circulation. 



The whole of the arteries of the systemic circulation proceed from a 

 single trunk, named the aorta, from which they are given off as branches, 

 arid divide and subdivide to their ultimate ramifications, constituting the 

 great arterial tree which pervades, by its minute subdivisions, every part 

 of the animal frame. The mode in which the division into branches takes 

 place, is deserving of remark. From the aorta, the branches, for the most 

 part, pass off at right angles, as if for the purpose of checking the impetus 

 with which the blood would otherwise rush along their cylinders from the 

 main trunk ; but in the limbs a very different arrangement is adopted ; 

 the branches are given off from the principal artery at an acute angle, so 



* To Galen is due the honour of having discovered that arteries contained blood, and 

 not air. 



