Page:Natural History Review (1861).djvu/333

Rh the same might be done for the arterial system by means of these isolated injections, and most beautiful and instructive preparations can be obtained by injecting, with differently coloured materials, the arteries of the conjunctiva, the mucous membrane of the nostrils, or the lining membrane of the mouth, pharynx, urinary bladder, &c.

The following results of a long series of such injections may merit attention, as some of them are of high practical importance.

When a single coronary artery of the heart is injected, the other (say the right) remains empty, showing that there is no anastomosis between the primary, or secondary, ramifications of these two arteries, in the circular and longitudinal grooves of the surface of the heart, as all anatomists say they have observed. When the injection passes from one artery to the other, it is always through the intervention of the capillary system that the communication takes place; never through the non-capillary system; hence it follows, that the right and left hearts are, to this extent, independent as far as regards their arterial circulation.

The same is likewise the case with the right and left lingual arteries. When the right lingual artery is injected with colouring matter, only one-half of the tongue becomes coloured, the other half remaining as it is. If the assumed anastomosis really existed between the two arteries (forming an arch in the top of the tongue) the injection of the one artery would certainly fill that of the opposite side.

When the Arteria laryngea superior is separately injected, it is necessary to put a ligature on the Art. thyreoidea inferior of the same side, because there is a very extensive anastomosis between the former and the laryngeal branch of the latter; this anastomosis will be found in the interior of the larynx (between the thyroid and cricoid cartilages); perhaps this fact admits of, the following interpretation: The superior laryngeal artery is not exposed to muscular compression, but the inferior thyroid, which gives a branch to the larynx, may occasionally be compressed by vehement contraction of the muscles under which it wends its way. The intra-laryugeal anastomosis of both is so arranged, that the necessary supply of blood cannot be stopped by such compression.