1906.] CYCLOPIA IN OSSEOUS FISHES. 445 



increased as also has the lens. The lens-cavity is not completely 

 occupied by fibres, a space being left anteriorly which is filled by 

 small round cells. Retina, choroid, cornea, vitreous humour, and 

 sclei'otic are well developed. The single choroidal fissure leads 

 back to a large optic nerve formed, as above stated, by the union 

 of the two optic tracts (fig. 4). There are two choroidal glands, 

 one on either side of the optic pore. They are supplied, as usual, 

 by choroidal arteries coming from the pseudobranchs. The fol- 

 lowing eye-muscles are present : — two superior obliques, arising 

 from the supra-orbital bars; two superior recti, arising along with 

 two inferior recti from the fibrous capsule of the brain in front of 

 the hypophysis ; two external recti, which are normal in origin and 

 are inserted into the right and left sides respectively of the eyeball. 

 The inferior recti are united close to their insertion into the 

 eyeball. Inferior obliqui and intei-nal recti are absent. 



(B) Cyclopia loith Fusion of Structures in the Mid-hrain and 

 of the Cerebral Lobes. 



Three of my specimens exhibit this condition, two of them 

 possessing a single median eye, Avhile the third, although showing 

 the other essential features of cyclopia, has a pair of small closely- 

 approximated eyes. 



1. The specimen which has a single eye resembles type A in 

 general appearance, except as regards its mouth-parts. In place 

 of the lower jaw there is a membranous flap on either side 

 projecting downwards and forwards from below the eye. In 

 place of the lower jaw arcade there is a narrow mesial process 

 projecting forwards to end just between the flaps. Microscopic 

 examination of the flaps shows that they contain externally a 

 number of young teeth and internally a commencing membranous 

 ossification. They are probably to be compared with ununited 

 maxillary processes, and in this respect they resemble the liorn- 

 like structures found by Paolucci* in his cyclopean Skate. 



The mesial process above mentioned contains a much elongated 

 symphysis of the lower jaw, the Meckel's bars of which diverge 

 little from one another and articulate with suspensoria which are 

 similarly apj)roximated. 



Skeleton. — The trabeculse cranii are represented by a single 

 exceedingly short bar projecting downwards and forwards towards 

 the wall of the pharynx. Quite separate from this are the palato- 

 quadrates, the anterior ends of which, uniting below the eye, form 

 a mesial plate replacing the defective trabeculee. The supra- 

 orbitals are difierent in the two specimens: in one they unite 

 anteriorly in the frontal process, giving rise to a small olfactory 

 capsule ; in the other they ai-e shoit and extend no further 

 forward than the middle of the fore-brain. In this latter case 



* AUi deJla Socicta Italiana di Science Natural!, vol. -wii, 1874. 



