EYE OF THE ENGLISH SPARROW 353 



man. When the relative size of the eye and the brain of the 

 bird and man are compared a great difference is notedr This is 

 graphically shown by Putter ('12). Leuckart (76) finds that 

 the weight of both eyes of some birds is greater than their brain 

 weight. I have found this to be true in a young eave swallow 

 (Chelidon ery throgaster) , just able to fly, whose brain weighed 

 .521 gram and the two eyes .625 gram. The brain weight thus 

 forms a ratio to the combined weight of the eyes of approxi- 

 mately 5 to 6. In the California blue jay (Aphelocoma cali- 

 fornica) I have found the brain weighs 3.433 grams and the two 

 eyes 2.613 grams. In the sparrow I have also found that the 

 reverse is true, for the brain weighs almost two and one-half 

 times as much as the two eyes. The average weights are: 

 brain, 1.0803 gram; the two eyes, .4455 gram, a ratio of brain 

 weight to eye weight of a little more than 2.4 to 1. The weight 

 of the human brain is many times the combined weight of the 

 two eyes. Making use of Vierordt's ('93) tables of weights of 

 these two organs, we find that the ratio of brain weight to that 

 of the eyes is 51 to 1. 



Since the lids cover the greater portion of the eye of the bird, 

 its large size is not apparent until it is fully exposed. Figure 8 

 shows the skin and lids dissected loose and turned forward, 

 exposing the eye. The equatorial diameter of the sparrow eye is 

 7.4 mm. and the axial diameter is 6.8 mm. The similar dimen- 

 sions of the human eye are 24.5 nmi. and 24 mm., respectively. 

 The relative size of the sparrow and the human eye is diagram- 

 matically shown in figure 1. The ratio of the radius of curva- 

 ture of the cornea to that of the posterior part of the eye is 

 approximately 1 to 2j. Man shows a ratio of about 4 to 5. 



The two eyes are so situated as to almost touch each other at 

 the median plane (figs. 12, 18, and 19). The eye socket is very 

 shallow. The eyeball, extrinsic muscles, blood-vessels, nerves, 

 and glands practically fill the socket, leaving httle room for 

 adipose tissue. The bony portion of the anterior part of the 

 orbit extends but slightly beyond the equator of the eye. The 

 posterior portion, however, reaches almost to the junction of the 

 sclerotic and cornea. 



