27$ GENERAL ANATOMY. 



abdomen the sheath of the arteries is in part formed by the 

 serous membranes. That of the spermatic arteries is remarka- 

 ble for its looseness, and that of the arteries of the brain is not 

 distinct. This part of the anatomy of the arteries, deserves 

 particular consideration in pathology, and in performing opera- 

 tions. 



409. The texture of the arteries* results from several su- 

 per-imposed membranous layers. There has been much di- 

 versity of opinion with reference to their number, it being sup- 

 posed to be, even as far as five by some anatomists, and re- 

 duced to one by others. It may be fixed at three, namely: 

 an outer, a middle, and an inner. 



410. The external membrane, called also, cellular, ner- 

 vous, fibrous, &c. , is thin, and of a whitish colour, and formed 

 of oblique and crossed fibres, interlaced diagonally with refer- 

 ence to the length of the vessel. Externally this tissue is ra- 

 ther loose, and adheres to the sheath; internally, on the con- 

 trary, the little fibres are so close that they can only be per- 

 ceived on tearing them asunder. In the arterial trunks, this 

 two-fold disposition is so distinct, that the outer layer really 

 appears double; in the middle sized and small arteries, on the 

 contrary, this layer becomes uniformly close and distinct from 

 the cellular tissue of the sheath, and then greatly resembles 

 the ligamentous tissue. 



This membrane is very tough and very elastic, both in its 

 longitudinal and circular direction. Supple and possessing 

 great strength at the same time, it is not divided by the action 

 of ligatures, even when directly applied to it. When we at- 

 tempt to tear it, great difficulty is experienced, and the texture 

 of its oblique fibres is perceived, which render its tenacity 

 equal in all directions. 



411. The middle membrane, called also muscular, ten- 



* Ludwig 1 , de Jlrteriarum titnicis, Lips. 1739. Albinus, acad. annot. lib. iv. 

 Cap. viii. de arterisR membranis et vasis. A. Monro, Remarks on the coats of 

 arteries, their diseases, &fc., in his works- Delasone, sur la structure des arte- 

 res, mtm. de Facad. des sci. 1756. C. Mondini, de JLrteriarum tunicis, in 

 opusculis sdeniifici t. i. Bologna, 1817. A. Beclard, sur les Blcssures des 

 cu'teries, Mt'm. de la sod. mcd. d 1 emulation, t. viii. Paris, 1817. 



