542 MULLER ON THE STRUCTURE OF THE GANOIDS. 
which have a true prolongation of the heart upon the arterial 
trunk, the muscular structure which lies external to the artery 
terminates with a sharp border, and the artery proceeds with its 
tunics within the muscular ring. On the contrary, the apparent 
muscle of the bulb of the osseous fishes continues uninterrupt- 
edly upwards, merely becoming thinner. The mass of the bulb 
consists entirely of these gray bundles, which internally form 
irregular ¢rabecule carnee, partly running obliquely, partly lon- 
gitudinally, but externally they form a very thick transverse 
layer. The inner layer gradually disappears superiorly, the trans- 
verse bundles are perceptible on all parts of the artery as com- 
pletely coherent layers, and may also be prepared in large fishes, 
as the Salmon, on which these examinations may be instituted. 
The gray lamina is internally covered by a thin coat, which 
mostly consists of undulating zigzag fibres; the thick white 
elastic layer, which lies externally to the gray layer, is also 
formed in the same manner. These are the unbranched elastie 
fibres which I described in the Vergl. Angiologie der Myzi- 
noiden. The gray lamina in osseous fishes exists quite sepa- 
rately, and their bundles are not entangled with the white elastic 
fibres. 
The bulb of the osseous fishes can therefore only act like the 
same layer in the general arterial system, but in a much greater 
degree. The Cyclostomi have not the dilatation of the walls into 
a bulb. Their difference from the osseous fishes, with which 
they agree in the position and number of the valves at the arte- 
rial mouth of the ventricle, is thus explained. But even in osseous 
fishes the formation of the bulb varies considerably. I have here 
merely pointed out the general results of the physiological de- 
velopment of this subject. I shall subsequently treat of it more 
specially when I have completed various experiments upon the 
vital properties of the lamina in question, in which I am now 
engaged, and when a chemical examination of it has been made. 
We shall thence ascertain whether the substance of the bulbus 
and its continuation is merely elastic, or if it also possesses a 
certain amount of organic contractility, which I imagine to be 
the case, although I have hitherto sought for it in vain. I shall 
then likewise describe the knotty vascular glomeruli which cover 
the heart of the Sturgeon, and, connected with the coronary ves- 
sels, are imbedded in the lymphatic cavities. 
