ARTERIES. 



[ 75 ] 



ARTIIROBOTRYS. 



In the largest arteries, the epithelial cells 

 of the inner coat are not so elongated, and 

 the inner coat consists principally of layers 

 of a homofyeneous, striated, or even di- 

 stinctly tibrillar substance, agreeing with 

 areolar tissue, traversed by finer and coarser 

 longitudinal networks of elastic tissue. Im- 

 mediately beneath the epithelium the net- 

 works or elastic fibres are either very fine, 

 or are replaced by one or more striated 

 layers, vrhich, when nucleated, often appear 

 as if composed of fused epithelial cells, and 

 Avhen homogeneous resemble pale elastic 

 membranes. The middle coat contains, as 

 a new element, elastic membranes or plates, 

 as many as 50 or GO, which, except in their 

 transverse direction, resemble the elastic 

 inner coat, sometimes forming the densest 

 networks of elastic fibres, at others fenes- 

 trated membranes. These layers alternate 



Fig. 36. 



Magnified 30 diameters. 



Transverse section of the human aorta below the superior mesenteric ar- 

 tery, after acetic acid. 1. Inner c«at: a, epithelium ; 6, striated layers ; c, 

 elastic layers. 2. Middle coat : d, its elastic layers ; e, the muscular and 

 areolar tissues. 3. Outer coat with its network of elastic tissue. 



with those of the muscular fibres traversed 

 by areolar tissue and networks of elastic 

 tissue. The muscular layer of the middle 

 coat is less developed, its cells smaller and 

 less regularly and perfectly formed. 



The outer coat is relatively and absolutely 

 thinner than that in the smaller ; but the 

 structure is the same, except that its inner 

 elastic layer is much less developed. 



In some of the larger arteries of man, as 

 the axillary and popliteal, and the mesenteric 

 arteries of other mammals, the internal coat 

 contains unstriped muscular fibres. This 

 is the case also with the outer coat of 

 the larger arteries in animals, but not in 

 man. 



All except the smallest arteries are fur- 

 nished with nutrient blood-vessels, the vasa 

 vasorum ; these ramify principally in the 

 outer 



coat, in the larger ones extending into 



the middle coat. They also receive branches 

 of the sympathetic and spinal nerves. 



Transverse sections of the arteries are 

 best made with the freezing section-cutter 

 or microtome. The epithelial cells require 

 the use of solution of nitrate of silver. 



The most important patliological changes 

 to which the arteries are subject, consist of 

 the deposition of fat in their substance 

 (fatty degeneration) and of atheromatous 

 matter. These will be noticed under Fatty 



DEGENERATION and ATHEROMA. See 



Vessels. 



BiBL. Heule, Allg. An.; Kolliker, Geive- 

 helehre ; Wedl, PatJi. Hist. ; Rokitansky, 

 Krankh. d. Art. ; Frey, Histologie, 1881 ; 

 Eberth, Strieker's Handlmch, v. p. 190; 

 Rutherford, Hist. p. 100 ; ColwikQim, Pathol. 

 1878, p. 1(38. 



ARTHO'NIA, Ach.— A genus of Li- 

 chenaceous Lichens, tribe 

 Grapliidei. 



Char. Thallus thin or 

 subepidermal and evanes- 

 cent ; apothecia dark, in- 

 nately sessile ; asci pyri- 

 form ; spores 4-8, septate, 

 upper cell larger ; no para- 

 physes. 



32 species, some common ; 

 on trees, holly, ash, oak &c. 

 BiBL. Leighton, Lich. 

 Flora, 1870, p. 414. 



ARTHRIN'IUM, Kze. 

 • — A genus of Dematiei 

 (Ilyphomycetous Fungi), 

 of which one species has 

 been found in Britain, 

 growing upon dead leaves of Eriophorum 

 angustifolium. 



A. sporophlceum, Kze. 



Filaments elon- 

 gated, tufted, often not more than 1-50" 

 long, but frequently confluent in a linear 

 form, with a kind of velvety surface; spores 

 numerous,angular, or like a double cone, at- 

 tached in whorls at the joints of the filaments. 



BiBL. BQxk(i\ej,Ann.X.H. 18:i8, i.p. 436 ; 

 Torula Eriophori, Berk. Enql. FL v. pp. 2, 

 359 ; Fries, Sum. Veg. p. 502. 



ARTIIROBOTRYS, Corda.— A genus 

 ofMucedines ( Hypho my cetous Fungi) bear- 

 ing elegant nodular groups of septate spores. 

 No species is yet recorded in Britain. 

 Corda describes one species, A. superha (fig, 

 37) ; in this the spores are about 1-1500" 

 long. Fresenius describes another, A. oligo- 

 spora, perhaps not distinct, which has the 

 erect filaments about 1-50" high, solitary,. 



