The following observations are to be regarded as supplemental to the preceding article.
There is no fact more worthy of the atten tion of the practical surgeon, as regards the anatomical history of the carotid artery, than the free anastomosis which exists between the external and internal carotids of both sides at nearly all the stages of their course. This is especially the case with the external carotid arteries which anastomose at numerous short intervals from their origin to their termination, where they likewise communicate with some small ramifications of the internal carotids. Nor is the communication between the internal carotids less free, although it is less frequent : this communication is formed within the cra nium at the anterior segment of the circle of Willis. Moreover, by means of the posterior communicating artery the internal carotid anas tomoses with the posterior cerebral, and there by with the subclavian, through the medium of the vertebral artery. And farther, by the anas tomoses of the superior thyroid artery with the inferior, and of the occipital with the cervicalis ascendens, profunda, and vertebral, a commu nication is established between the external carotid artery and the subclavian.
From the knowledge of the communication thus existing between these several portions of the arterial system of the neck and head, we may deduce some very useful inferences.
1. It is evident that the carotids of both sides may be injected by even a coarse injec tion, from a pipe introduced into the artery of one side. This is a fact well known to every practical anatomist.
2. With the knowledge of this freedom of communication between the carotids, no sur °eon will look for uniform success filter the application of a ligature, in cases of wounds of either carotid or of one of its branches, if the ligature be applied only below the situ ation of the wound. Nevertheless, experience tells us, that such a plan of treatment has been successful in several instances; and it is wor thy of notice that in almost all the successful cases the primitive carotid was tied very shortly after the infliction of the wound, at a time when the collateral branches could not have become sufficiently enlarged to admit of the full circulation in them ; while, on the other band, in two unsuccessful cases, the primitive carotid was not tied for some days after the receipt of the wound, and secondary hemor rhage ensued in each case.
3. The free anastomosis of the two internal carotids with each other and with the sub clavians through the vertebrals within the cra nium, sufficiently evinces that the circulation of the brain after the obliteration of either carotid, by ligature or otherwise, may be easily maintained ; and experience fully confirms this inference from anatomy. That a disturbance
of the cerebral circulation does occur occa sionally after the operation of tying the carotid is fully proved ; but it would appear that it is an occurrence much more rare than might, a priori, be expected. Of seventy cases, col lected by Berard,* in which this operation was performed, symptoms arising from cerebral affection appeared only in a very few, and in two only of these instances the patients died from the effect produced upon the cerebral cir eulation. One of these cases occurred in the practice of Mr. Aston Key ; the patient fell into a deep sleep after a severe fit of coughing, and died shortly afterwards without awaking. On examination it was found that the carotid of the opposite side was obliterated by a co-. agulurn nearly as low as its origin from the 'aorta, so that the cerebral circulation could only have been maintained by the two vertebral arteries, which in this case were smaller than usual. In the second case, which was ope rated on by Langenbeck,t immediately after the application of the ligature the patient be came motionless, with closed eyes, without speaking, except when addressed several times in succession ; he sank gradually, and died in thirty-four hours after the operationl In three of the cases collected by Berard, some disturbance or indistinctness of vision, on the same side as that on which the artery was tied, followed the operation; in one of these the impairment of sight was accompanied by syncope, and a sensation of cold affecting the whole of that side of the face; In a second, related by Mr. Mayo, the impaired vision was only on the right side, the carotid of which side had been tied, and the sense was perfectly restored in a few hours. In the third case one eye was completely deprived of sight, and the sense of hearing greatly weakened in the ear of the same side. Berard remarks that the loss 9r impairment of vision on one side is un favourable to the opinion that such an occur rence is to be attributed to disturbed cerebral circulation ; it is sufficiently accounted for by the fact that there is a considerable diminution in the quantity of blood sent to the eye ; for that organ is supplied by a direct branch of the internal carotid, viz. the ophthalmic, which anastomoses at its termination with several of the terminal branches of the arteries of the face; and it is not improbable that in the cases above referred to, the branches which form this anastomosis, as well as those forming the circle of Willis at the base of the brain, were much smaller than usual.