446 DR. J. F. GEMMILL ON [Api\ 10, 



the olfactory region is destitute of cartilage and there is no tegmen 

 over the third ventricle. In both specimens the supra-orbitals 

 are displaced downwards so as to be ventro-lateral to the brain. 

 The auditory cartilages are displaced similarly but to a slighter 

 degree. 



Brain. — The cerebral lobes are markedly reduced in size and 

 are fused togetlier, the longitudinal fissure being almost entirely 

 absent. The central cavity is slightly enlarged and extends 

 downwards on the outer sides of the lobes further than in the 

 normal condition. The pineal diverticula are small unstalked 

 pouches. The optic lobes are of considerable size and are normal 

 as regards their dorsal parts, but internally the me;^'lal furrow of 

 the central canal is only slightly marked (fig. 5) and there is 

 absence alike of the optic recess, of the hypophysis, and of the 

 hypoaiia. Optic tracts and nerves are absent. As in type A, 

 the olfactory nerves are small and closely approximated. 



Eye. — The single small deeply embedded eyeball has no choroidal 

 fissure, vitreous humour, or optic nerve. The lens and the retina 

 are, however, fairly well developed and there are two choroidal 

 glands. The position of the optic pore is marked inside the eye- 

 ball by an inteiTuption of the retina exhibiting a few nerve-fibres, 

 which, however, fail to pierce the hexagonal pigment-layer on the 

 sclerotic (fig. 6). Two external and two superior rectus muscles 

 are present. The other eye-muscles are wanting, with the exception 

 of a pair of small superior obliques found in the specimen men- 

 tioned as having its supra-orbital bars extending forward into the 

 frontal process. 



Mouth. — The mouth-opening is represented by a minute canal, 

 beginning at the bottom of the groove between the maxillary flaps 

 and extending backwards above the symphysis of the lower jaw. 

 In one case this canal ends blindly, in another it joins the 

 pharynx. 



2. The specimen which had two small eyes closely approximated 

 but ununited shows the following characters : — cerebral lobes 

 well developed, deeply cleft anteriorly, but united posteriorly ; 

 pineal diverticula small ; third venti-icle almost obliterated ; 

 fusion of structures in the floor of the optic lobes ; rudimentary 

 hypophysis and hypoaria ; optic tracts and nerves absent ; 

 eyes small, embedded, almost touching one another, without 

 choroidal fissure, vitreous humour, or optic nerve, but with 

 well-developed lens, retina, and retinal pigment-layer ; superior 

 obliqui, superior and external rectus present for each eye, 

 inferior recti and obliqui wanting ; no mouth, the upper and 

 lower jaws being sealed together; trabeculse cranii extremely 

 short, forming a single bar projecting downwards and forwards 

 into wall of pharynx ; olfactory capsules absent ; supra-orbital 

 bars ending separately in front, the tip of each giving origin to an 

 obliquus oculi superior ; olfactory pits approximated and supplied 

 by small olfactory nerves. 



