482 



THE BLOOD-VESSELS. 



[sect. 213. 



Fig. 194. 



No. 6). Ganglia occur not only in the cardiac plexus at different 

 places, but also, as Remak discovered in the calf, in the muscular 



substance of the auricles and ventricles, 

 and the same holds good for man and 

 other animals. These ganglia are best 

 known in the frog, where they are seated 

 especially in the septum and at the junc- 

 tion of the auricles with the ventricles, 

 and they contain apolar and unipolar cells 

 {Ludwig, Bidder, R. Wagner, and myself) . 

 The small fusiform swellings upon the 

 outer nervous branches, especially de- 

 scribed by Lee, are not ganglia, but only 

 thickenings of the neurilemma. 



Diagram of the left ventricle, 

 with the septum, for the pur- 

 pose of indicating the course of 

 the muscular fibres, a, a, a". 

 superficial fibres: a. on the an- 

 terior wall ; a. their course in- 

 wards at the apex of the heart ; 

 a", passage of the same into the 

 posterior papillary muscles ; 

 b,b',b". septal fibres of the right 

 side ; b. in their course down- 

 wards and forwards ; V . their 

 pas-age into the apex of the 

 heart, and internal muscular 

 layer of the left ventricle, as 

 also their termination in the 

 anterior papillary muscle, b" ; 

 c — c"". middle muscular layer ; 

 c. commencement from the right 

 side of the ostium, and course 

 on the anterior wall obliquely 

 downwards to the left and pos- 

 teriorly ; c. curve at the septum 

 and course therein ; c", c". curve 

 at the anterior wall, and course 

 in the deeper portion of it, up to 

 their termination in the ostium 

 venosum, c"". 



II. — Of the Blood-Vessels. 



§ 213. The blood-vessels are divided, 

 with reference to their structure, into 

 arteries, capillaries and veins ; yet these 

 three divisions are by no means broadly 

 separated from each other, inasmuch as 

 the capillaries are continued into the veins 

 just as imperceptibly as they arise from 

 the arteries. On the other hand, the 

 two kinds of larger vessels, although con- 

 structed upon a generally similar plan, 

 are sharply and definitely distinguished in 

 many points. 



With reference to the tissue composing the vessels, and its ar- 

 rangement, the following general remarks may be made. While 

 the true capillaries possess only a single coat, without any struc- 

 ture whatever, the larger vessels present, with few exceptions, 

 three principal layers, which may be most fittingly designated as 

 the inner coat, or tunica intima ; the middle coat or circular 

 fibrous coat, tunica media; and an outer coat, tunica externa s. 

 adventitia. The membrana intima is the thinnest coat, and in- 

 variably consists of a cellular layer, the epithelium ; generally also 

 of an elastic coat, with the fibres disposed principally in the longi- 

 tudinal direction ; and to this again other layers of various kinds 

 may be superadded, which likewise almost invariably retain the 

 longitudinal direction. The tunica media is mostly a thick layer, 

 and is the principal seat of the transverse elements, and of the 



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