ANATOMY OF THE FUNDUS ORGANS IN BIRDS 



25 



incomplete dissection of the parts and may 

 be modified later. 



In this judgment, if we read him aright, 

 Treacher Collins, to some extent, concurs. 

 In his Erasmus Wilson Lectures on the Anat- 

 omy and Pathology of the Eye he remarks 

 that "in other animals than Mammals and 

 in the human fetal eye there are sources of 

 nutrient supply to the intraocular structures 

 in place of or in addition to the ciliary body." 

 He adds that the pigmented, plicated struc- 

 ture of the bird's pecten "closely resembles 

 the choroidal coat . . . having, however, 

 a rather finer capillary plexus. Birds, there- 

 fore, not only possess well-formed ciliary pro- 

 cesses but also a special vascular arrangement 

 in the vitreous chamber." 



According to O. Zietzschmann, also, the pec- 

 ten is covered by a delicate membrane which 

 is continuous with the inner 

 limiting membrane of the retina. 

 The bloodvessels, according to 

 him, belong to the ciliary sys- 

 tem and are branches of those 

 supplied to the optic nerve. 

 Leber believes the pectinate ar- 

 tery to be the homologue of the 

 hyaloid artery. 



Finally, it may be added that 

 there are no bloodvessels in the 

 Birds' retina and the vessels of 

 the pecten do not, consequently, 

 arise from a central artery of 

 the optic nerve as in Mammals 

 since that, too, is wanting. 



This arrangement, inasmuch 

 as the opaque vessels do not, 

 as in most Mammals and other 

 Vertebratse, intercept the rays 

 of light impinging on the per- 

 cipient elements of the retina, makes for a 

 more distinct and measurably clearer-cut 

 image of the object visualized by the avian 

 brain. 



Comparative ophthalmoscopy of reptilian 

 fundi. With the aid of Mr. Head's brush and 

 by courtesy of Dr. Lindsay Johnson the writer 

 is able to compare a few typical fundi of 

 Reptiles with those of their ancestral cousins 

 the Birds. 



It requires only a glance at these pictures 

 to feel assured that the eyes of that nocturnal 

 reptile the Turkish Gecko (Plate LIX), 

 whatever else may be said on the subject, 

 are more decidedly avian or, rather, more 

 ornithosaurian than are those of the Horned 

 Toad (Plate LX), or Indian Cobra (Plate 

 LXI), whose fundi belong more distinctly to 

 other vertebrate types. These last-named 

 possess definite retinal vessels (that issue 

 from a circular optic papilla), and they have 

 no pecten or at least the mere suggestion of 

 one. Compare Plate LXI with Fig. 143; 

 and Plate LX with Fig. 144, which show 

 the resemblance between the Cobra fundus 

 and that of the Hedge-Hog, while the eye- 

 ground of the Horned Toad suggests that 

 of the Virginian Opossum. For further com- 

 parison a diagram of an ichthyan fundus 



Fig. 14 



Ophthalmoscopic View of the Fundus of the Fish Gadus merlangus. 

 (After Beauregarde.) The processus falciformis (black) runs the whole 

 length of the (white) optic nerve-head, at the peripherj' of which are seen 

 six branches of the hyaloid artery. 



oculi (Fig. 14) — that of Gadus merlangus — 

 is shown. 



If one may draw any conclusion from such 

 sparse material and from such an incidental 

 examination of the subject it is that whatever 

 of common origin the avian and reptilian 

 classes may have originally had the ornitho- 

 logical branch left the parent stem with a 

 subdivision of the Lacertilia and not with the 

 Ophidia. 



