| OCR Text |
Show 1897.] EYES O F T H E O R D E R PRIMATES. 1S5 most books which treat on the subject we find it stated that among mammals M a n and the Anthropoid Apes (the Simiidae) alone possess a macula ; but I find, as I will presently explain, that the existence of the macula is not restricted to these only. In addition to the scarlet and lake-red branches of the retinal vessels which proceed from the disc, a large number of interrupted orange-yellow and red vessels, uniformly coloured and much broader than the artery and the veins, can be observed, anastomosing so as to form a network (see cc, Plate V.). These vessels belong to the choroid, a vascular structure underlying the retina. As that portion of the retina which lies in contact with the choroid is pigmented, these choroidal vessels can only be distinctly observed in fair people and in albinos. I am, of course, speaking of the normal eye of the adult, and not taking into consideration defective senile or pathological conditions. It is not only with regard to the degree of distinctness with which the choroidal vessels can be observed that the ophthalmoscopic appearance differs in fair and dark people. The colour of the fundus likewise varies in proportion to the pigmentation of the individual. In very fair people the colour is a bright vermilion, which gradually tends towards a reddish brown in people with very dark hair and skin, until we find it of a chocolate colour in the negro. Except in colour, the appearance of the fundus oculi does not differ in the various races of Man. I need hardly say that of course the colour of the macula varies with the general colour of the fundus, being always distinguishable as a darker patch than the rest, although occasionally, in very dark Europeans, I have seen it of a decidedly redder hue than the rest of the fundus. The chocolate-coloured field, with a darker chocolate-coloured circular patch indicative of the macula region bordered by a bright scintillating ring, characteristic of the negro, is likewise what we find when we examine the eye of the Simiidae, but we find the fundus varies greatly in colour once we descend below this group. Even in the Gibbons, the lowest of the Simiidae, we already find a commencement of this departure. Throughout the Anthropoidae the arrangement of the retinal vessels is the same as in Man, the first indication of variation being found as soon as w e reach the Lemuroidae. The disc is oval, with the long axis vertical, at times more or less circular, or practically the same as in Man. Here again we only find a difference in the Lemuroidae, which all have a circular disc. The Lemuroidae have no macula, the existence of which ceases with the last of the true Monkeys. In other words, we find a striking resemblance between the appearance of the eye of Man and the entire order Anthropoidae, although in many details we can trace as we descend the scale a tendency towards that lower form which reveals itself to us when we examine the Lemuroidae; and here again we find a gradual departure from the higher type |
