' . /: \ 1:11. i /. ( <>\ SII>J:JIA TI<>.\ >-. 



519 



Fig. 268. 



Fig. 27U. 



::AII:I. MI.MIII: VM: 



Kr.oji TIII: CAROTID 



-v oi nu. iiORsi:. 



lied 350 diame- 



Fig. 269. 



on the >ne part, and on the other with the capillaries and veins. For a 

 lontr time it has been assimilated to a serous membrane, but it has not 

 al Cutely the same texture. It is composed of a simple epithelial layer 

 which is in contact with the blood, and is formed by fusiform cells that 

 slightly bulge in the situation of their nucleus. 

 These cells sometimes become detached, and are 

 carried about in the nutritive fluid, in which, after a 

 certain period, they resemble 

 more or less mis-shapen blood- 

 globules. The epithelium lies 

 upon a layer of amorphous 

 elastic tissue, perforated by 

 openings, and named tiicfcne- 

 .-'/?/"/ inriiilifdiie ; on its ex- 

 ternal face are proper elastic 

 fibres passing in a longitudinal 

 direction. 



The middle tunic is remark- 

 able for its thickness, its elas- 

 ticity, and the yellow colour it 

 offers in the principal vessels. 



It is composed of a mixture of elastic fibres, as well as 

 smooth muscular fibres, the first constituting a kind of 

 network, in the meshes of which the contractile fibres 

 are disposed in a circular manner around the vessels. 

 The proportion of these two 

 elements varies with the size 

 and situation of the artery. 

 In the large trunks, such as 

 the aorta, the elastic is more 

 abundant than the contractile ; 

 in the middle-sized vessels 

 they are about equal ; but in 

 the small arteries, in which 

 the contractile force of the 

 heart is lost because of their 

 distance from it, the muscular 

 fibres almost exclusively com- 

 pose the middle tunic. 



The cjrti'run} tunic is only 

 '' a layer of connective ti.~ 

 with some longitudinal reticu- 



lastic fibres in its <1< 

 part. Though this tunic is 

 very thin, yet it is strong; as 



a ligature tied tightly around an aitery will rupture 

 the other tunics, but not this. 



The structure of the ctipillnrii-* is n t the same 



(tjust described, but is modified in proportion as they are fine. In 



Ike H :ij)illaries, the walk are formed by a thin amorphous n.em- 



in which (oblong) nuclei are somewhat regularly disseminated; in 



/. 1 vessels, another layer containing t: mclci is . 



1 in tin- largest cani Marie.-, those imm- diatcly Micce. dinj: 



"I:K OF 

 HIIMH.I: co\r or 11 i.. 



i:V AIM'KRY OK 



. nil. l 11:1:1.- 



. i-n.i:<-i I- \v mi 



: OPI.NI-- 



Maz: lima- 



. ..i 



ii:\N>iriON OF A MINI 11; 



ARTERY OF THK 1 IIVIN 

 1XTO CAI'ILLAI:\ 

 SKLS. 



1, Minute artery; 2, Tran- 

 sit ii.nal cajiillii! 



wijiillary with 

 thick ci.at. repr- 

 l>y a iimil>li> contour 

 line; 4, Fine capillary, 

 with siu^'lo 0'iiti'ur. 

 The nuclei are seen 

 wM.-ly M-.itti-ivil iu 4 

 uli'l 9 : iy ruii- 



gregati-1 in -J ; am'l >till 

 M in 1, wlu-ru they 

 fiinii au t>|iithuliiun. n, 



niu-K'i uf inii>i-ular cells, 

 tin; ini -i|ii. ut iniix-ul.ir 

 coat of the artery. 



