MINUTE ANATOMY OF THE ARTERIES. 267 



1 have not been able to convince myself of the precise mode in 

 which they terminate, especially in regard to the muscles. 



Ganglion cells occur in the course of some of the afferent nerve 

 fibres, and in the coarser plexuses. Beale* considers them to 

 be very widely distributed. I have recognised them only in 

 the inferior vena cava of the Frog, where they were first dis- 

 covered by Lehmann.'f' Heaps of small, somewhat flattened, 

 and closely compressed ganglion cells unite to form roundish 

 nerve knots. 



ARTERIES. 



mu 

 ere 



The arteries are distinguished from the veins by their 

 thicker walls, resulting from the greater development of their 

 uscular and elastic fibres. The thickness of the entire wall in- 

 ases, though not proportionally to the increase of the calibre 

 of the vessel. The thickness of the muscular tissue increases 

 with the diminution of the calibre. The quantity of elastic 

 fibres, on the other hand, increases with the calibre. The 

 cellular layer of the arteries consists of fusiform or, occasion- 

 ally, polygonal cells, which vary but little in diameter in the 

 various vascular provinces. 



ELASTIC INNER COAT. The innermost layer of the exter- 

 nal vascular coat the elastic membrane of Bonders, the 

 elastic internal tunic of Kolliker, the elastic longitudinal 

 fibre layer of Remak consists in the finest vessels of a net- 

 work of fine elastic fibrils, or of a delicate structureless elastic 

 membrane, which, in collapsed or bent vessels, or when sepa- 

 rated from its attachments, exhibits fine parallel, longitudinal, 

 and transverse folds. It can be distinguished even in very fine 

 tubes possessing only isolated muscle cells. Towards the larger 

 vessels the membrane increases in thickness ; small rounded or 

 elongated spaces occur in it, and it now appears as a fenestrated 

 membrane thickened with longitudinal rugae (Arteria basilaris). 

 In the larger vessels the fenestrae are more numerous; the 



* Philosophical Transactions, cliii., p. 562. 

 t Zeitschrift fur wissenschaftliche Zoologie, Band xiv., p. 346. 



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