CYCLOPIA— STRUCTURE 41 



nerves. Posteriorly, the supra-orbital bars separate and pass along the dorso-lateral aspects of the 

 brain to join the auditory cartilages, as in the normal condition. Near their place of separation, each 

 gives origin to an obliquus oculi superior muscle. 



The mandibular, hyoid, and palato-quadrate bars are appreciably shortened in accordance with 

 the small transverse measurement of the mouth. 



Brain. The cerebral lobes are slightly smaller than normal, and are in great part united along 

 their inner faces. The median longitudinal fissure penetrates for only a third of their depth in front at 

 the place of origin of the olfactory nerves, while posteriorly, close to the third ventricle, the fissure in 

 question appears simply as a shallow groove. The third ventricle region and the optic lobes 

 are well developed, pineal diverticulum, optic recess, hypophysis, and hypoaria being present as in the 

 normal condition. A transverse section at the origin of the olfactory nerves shows an area of brain 

 which is - 66 of normal size as judged from a specimen of the same age. The proportion to normal 

 in a similar section at the back part of the cerebral lobes is - 95, while the middle region of the optic 

 lobes shows a sectional brain-area which is slightly in excess of normal. 



There is no dropsy of the central cavity of the brain or of the meninges. The cranial nerves 

 are all present and are normal, with the exception of the first two pairs, the olfactory nerves being 

 small and closely approximated, while the optic tracts unite at the commissure to form a single optic 

 nerve. 



Eye. The globe is large and has its transverse diameter 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. Ketina, choroid, cornea, vitreous humour, and sclerotic 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. 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 following eye-muscles are 

 present : two superior obliqui, 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 

 internal recti are absent. 



(B) Cyclopia with Fusion of the Cerebral Lobes and of Structures in the Mid-brain. 



Three of my specimens exhibit this condition, two of them possessing a single median eye, 

 while the third, although showing the other essential features of cyclopia, has a pair of small closely- 

 approximated eyes. 



1. The specimens which have a single eye resemble type (A) in general appearance, except as 

 regards their mouth-parts. In place of the upper 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 un-united maxillary processes, 

 while in appearance they resemble the horn-like structures found by Paolucci {181) in his 

 cyclopic ray. 



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 approximated. 



Skeleton. The trabeculae 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 trabeculae. The supra-orbitals are different in the two specimens : in one, they unite 

 anteriorly in the frontal process, giving rise to a small olfactory capsule; in the other, they are short 

 and extend no further forward than the middle of the fore-brain. In this latter case, the olfactory 



F 



