The Morphology of Cosmobia 417 



related lateral eyes, and probably to be accounted for in all by the 

 immaturity of the embryo. For the same cause none of the four has 

 as yet a tarsal cartilage, nor either a lacrimal nor a Harderian gland. 

 In the identification of the muscles the relative position of the ttvo eye- 

 halls must he constantly I'ept in mind, that is, that their anatomical 

 external aspects are adjacent to each other, and that they are thus not 

 related as a normal pair of eyes, hut just the reverse. 



Three of the eye muscles may be at once identified by their innervation ; 

 the superior oblique, innerved by the Trochlearis; the external rectus, 

 innerved by the Abducens; and the retractor bulbi, which is innerved upon 

 its external side by the Abducens and upon its internal by a branch of 

 the Motor oculi. Aside from the innervation the shape and other rela- 

 tions of these muscles is also characteristic and assists in the identifica- 

 tion; the superior oblique shows already the bend for the pulley along 

 the inner side of the eyeball, the retractor partially encloses the optic 

 nerve from the external side, and the two external recti lie upon the 

 external sides of the eyeballs, although the close proximity of the two to 

 each other crowds them together into a pair of closely associated slips, 

 united at their origin and somewhat reduced in size. 



The three other recti, superior, internus, and inferior, are sufficiently 

 distinguished by their relative position and by their innervation from 

 the Motor oculi; their relations are quite normal and they are equally 

 developed in both components. At the lower (posterior) aspect of each 

 eyeball is found the little obliquus inferior, arising from the side of the 

 nose of the same component, and running laterally to the eyeball. The 

 nerve supply to this muscle was not easy to determine from the sections, 

 but seems to be by means of small twigs that arise from the branch to 

 the inferior rectus and run along the anatomical outer side of the latter 

 muscle, that is, the relationship is normal. In the case of the lateral 

 eyes, which, owing to the slight lateral obliquity of the components, is 

 cut at a little different plane, the nerve supply to this muscle is easily 

 seen, and is also the normal onp. 



In Fig. 32, where the relations of the eye muscles in this and the 

 following Teras (XII) are compared, the conditions just described are 

 given in the form of a diagram. In this may be seen at a glance the 

 fact that the muscles of each eyeball are wholly normal and that the two 

 are perfectly symmetrical. 



The nerves that supply these muscles are as normal in origin and 

 course as the case will allow. The two Third and Fourth nerves come 



