The Morphology of Cosmobia 415 



side, immediately dorsal to the end of the cranial cartilage. The gan- 

 glionic mass which lies exactly in the middle, and from one side of which 

 a nerve issues that runs along the side of the Trochlearis, has nothing 

 directly to do with the eyeballs but represents a median componental 

 Trigeminus, which becomes much larger a little posterior to this section 

 (Gasserian ganglion), and sends out a stout nerve to each side. From 

 their relation to the adjacent parts these lateral branches prove to be the 

 Nasal branches of the Ophthalmic, which supply the inner sides of the 

 two components. The small median nerve, dorsal to this and seen in 

 cross-section, is the componental Abducens, which, like the Trigeminus, 

 arises too far back to possess two separate roots. It supplies the external 

 sides of the two retractores bulbi, and the small external recti, which lie 

 naturally in the middle between the two eyeballs and are fused at their 

 origins. 



The second section figured here, No. 250, is cut along the level of the 

 lateral eyes and involves the two snouts as well. In the dorsal part of 

 the section lies the medulla, showing certain indications of doubling, 

 in particular a ventral forking of the central canal. In front of this 

 lies the doubled median cartilage of the basis cranii, probably in the basi- 

 occipital region, containing two notochords, some distance apart. Upon 

 the sides of the skull are normally formed petrosal cartilages enclosing 

 sections through the labyrinth, but there is no indication, here or else- 

 where, of median ear components. Ventral to the basicranial cartilage 

 is placed the pharyngeal cavity, with portions of the recesses which, in 

 other sections, are seen to lead into the inner nasal cavities of each snout. 

 The obliquity of section through these latter organs corresponds to that 

 which appears in the other section in the case of the fore-brains, and 

 arises from the same cause, the oblique position of the axes of the later- 

 ally placed components. The various anlagen ventral to the pharynx 

 have not yet been identified. 



The details of the two inner eyeballs and their associated parts are 

 shown in Plate III, Fig. 7, and Plate IV, Fig. 8, which were drawn 

 almost directly from the nlodel of the region. Aside from these the 

 accompanying figure [Fig. 29] is of use to show the relationship be- 

 tween the eyeballs, the associated cranial nerves, and the brain. In this 

 the telencephalic lobes (hemispheres) of component B, the one nearest 

 the reader, are represented as partly rmoved, thus rendering visible the 

 median e3'es and other median parts. 



The two eyeballs consist of the left one of component A and the right 

 one of component B, so placed that the former is on the right and the 



