ARTERY. 



223 



maceration, the intervals between the fibres of a semilunar valve-like form, composed of a 



become greater, and as the putrefactive pro- duplicature of the lining membrane in which 



cess sets in and advances, the whole substance there is included a portion of the middle 



of the middle tunic takes on the form of a tunic ; the more acute the angle at which the 



spongy mass, and ultimately the fibres cease branch arises, the greater is the prominence of 



to be any longer discernible, having been re- this ridge; it is altogether absent where branches 



duced to the state of a soft pulp, while the arise at right angles, as in the case of the emul- 



cellular structure is rendered more evident, gent arteries, and where branches arise at ob- 



The following appears to us to be the rationale tuse angles to the trunk, it is found at their 



of the phenomena above described : the in- orifices on the side next the heart, 

 crease in thickness which the middle tunic at 

 first undergoes is owing to the cellular tissue 

 interposed between the fibres imbibing the 

 water in which it has been immersed, in virtue 



The aorta and pulmonary artery are each 

 provided with three valves at their origins from 

 the ventricles; these valves, called sigmoid or 



semilunar from their semicircular form, are 

 of its hygrometric property ; and the spongy attached by their inferior borders, which are 

 appearance observable after the maceration convex, to the margins of the semicircular 

 has been continued for a length of time, is the flaps or festoons, into which the edge of the 

 result of the cellular tissue having the property commencement of the middle tunic of the 



of resisting decomposition by putrefaction artery is divided ; the superior edges of each 

 much longer than the fibrous tissue. 



The internal tunic (intima of Haller) is the 

 thinnest of the three ; it is continuous with 

 the lining membrane of the heart, in extending 



of these valves, which are free and floating, 

 form two concave lines, separated by a 

 projection in the centre, in which is con- 

 tained a small cartilaginous body, called 



from which into the arteries it forms a dupli- tubercle, globulus Arantii or corpus sesa- 



cature, contributing to the composition of the moideum. The portions of the walls of the 



semilunar valves : in the larger arteries, when artery corresponding to the valves are dilated 



empty, it sometimes forms longitudinal folds ; in the form of pouches, more marked in the 



in some arteries, such as the poplitaeal, and the aorta than in the pulmonary artery ; these are 



brachial at the bend of the elbow, it presents the sinuses of Valsalva. The semilunar valves 



transverse folds or wrinkles ; it also forms are composed of a dupticature of the lining 



transverse wrinkles in arteries which have re- membrane of the artery, including within it a 



tracted after amputation : its internal surface, thin but strong fibrous expansion, continuous 



which is in contact with the blood in the living with the fibrous structure, which connects the 



body, is smooth, polished, and bedewed with middle tunic of the artery with the tendinous 



a fine exhalation; its external surface adheres ring encircling the arterial opening of the ventri- 



to the internal surface of the middle tunics in cle; the free border of each valve contains a small 



the larger trunks of the arteries ; this tunic fibrous cord, as described by Beclard, having 



may be divided into two layers, the internal the globulus Arantii attached to it in its centre, 



of which is thin and transparent, while the An increase or diminution in the number of 



external is whitish and opaque, having its struc- the sigmoid valves is of rare occurrence, more 



ture blended with that of the middle tunic ; frequently presented in the pulmonary artery 



it is the tunica cellulosa interior of Haller, than in the aorta, and oftener consists in the 



and is the seat of the calcareous, steatomatous, number of valves being increased to four than 

 and atheromatous deposits, which so frequently 

 occur as morbid appearances in the coats of 

 the arteries. We do not perceive fibres nor 

 any other signs of organization in the inner 

 layer of this tunic in its healthy state ; it is 

 almost completely inelastic and very brittle; 

 it tears with equal facility in every direction ; 



diminished to two.* 



The mechanism of these valves is such as to 

 prevent the blood flowing in a direction con- 

 trary to its regular course ; for when that fluid 

 is propelled towards the ventricle, they are 

 separated from the parietes of the artery, and 

 being distended by the column of blood pres- 

 compared with other structures it bears the sing against their superior surfaces, they are 



.1 i i **. * i i i 



closest resemblance to the arachnoid mem- laid across the area of the vessel, which they 

 brane of the brain ; the smooth and highly completely fill up by their edges being thus 

 polished condition of the free surface of this brought into perfect contact and the globuli 

 tunic is an admirable provision, whereby the Arantii meeting in the centre. There are no 

 effect of friction in diminishing the velocity valves in the arteries in any other situation, 

 of the passage of the blood through the arte- The arteries, like other organized struc- 

 ries is reduced to the smallest possible amount, tures, are furnished with proper nutritious 



arteries and veins called vasa vasorum. The 

 aorta and pulmonary artery at their commence- 

 ment receive some branches from the coronary 

 vessels of the heart ; in all other situations the 



The following mechanical contrivance ob- 

 servable in the interior of the arteries would 

 appear to be a provision for facilitating the 



distribution of the blood through the divisions 

 of the arterial system. As the branches of the 

 arteries mostly arise from the trunks at acute 

 angles, the portion of the circumference of 

 their orifices on the side next the heart is 



vasa vasorum are supplied by the neighbouring 

 bloodvessels ; the vasa vasorum are very evi- 

 dent in the external tunic of the arteries, they 

 can be traced until they penetrate the sub- 

 smooth and depressed, forming a sort of chan- stance of the middle tunic, but not farther ; 

 nel sloping gently from the trunk into the 



branch, while the opposite side, or that more * Meckel, Handbuch der menschlichen Anato- 

 remote from the heart, is bordered by a ridge mie. Band. i. 



