8 DR. J. F. GEMMiLL OX [May 12, 



posterior fontanelle is much larger than in a normal case (PI. I. 

 fig. 4, /3). Each nasal cartilage is connected with a pair _ of 

 palato-quadrate bars, the inner or adjacent elements of which 

 converge, fuse, and end abruptly without being attached to a 

 suspensorium ; the outer bars are continued backwards on either 

 side, and articulate with the hyomandibulars attached to the 

 auditory capsules. Articulating with the united part of the 

 inner palato-quadrate bars is a small twisted piece of cartilage, 

 which passes downwards in the septum between the two mouth- 

 openings, and represents an inner or adjacent pair of Meckelian 

 cartilages. Dorsally, each nasal capsule is continuous with a pau- 

 of supraorbital bars, of which the outer elements pass backwards 

 on either side to join the auditory capsules, while the inner or 

 adjacent elements are connected with each other and with the 

 outer bars over the pineal body. Behind this the adjacent bars 

 disappear, the result being that over the region of the cerebral 

 lobes there are two small anterior f ontanelles, while over the optic 

 lobes there is a single large middle fontanelle (PI. I. fig. 4). The 

 hyoid bars and the branchial cartilages are normal, except that 

 they diverge rather more widely than is usual. Each arch, how- 

 ever, may be looked upon a,s being composite, i. e. as consisting of 

 the outer elements of a double set of arches. The suspensoria on 

 either side of the two periotic capsules are normal. 



As mentioned above, the notochord is double in front, two 

 notochords being present as far back as the fourteenth body- 

 segment. These converge together at an acute angle and finally 

 imite. The condition of the neural and hsemal arch cartilages is 

 illustrated in PL I. fig. 8. Where the two notochords are some 

 little distance apart, the inner or adjacent neural arches are dis- 

 placed so as to form a floor for the transversely-expanded spinal 

 cord, while the inner hfemal arches remain as small nodules of 

 cartilage. As the notochords come closer together the inner 

 neural and hfemal arches alike disappear, while the outer arches 

 assume a normal form and position. 



The bi-ain and its cavities show a degree of duplicity which is 

 indicated diagrammatically in PI. II. fig. 15. There are two pairs 

 of cerebral lobes and two thalamencephala, diverging forwards 

 from a single composite optic lobe region. The cerebral lobes and 

 thalamencephala, besides diverging, are rotated slightly in such a 

 way that they lie closer together dorsally than ventrally. There 

 are two pairs of olfactory nerves, two pairs of optic nerves, and 

 two sets of pineal diverticula. There are also two infundibula, 

 which converge as they pass downwai-ds and backwards. Each 

 ends in a hypophysis sac after giving off the usual diverticula for 

 the hypoaria (PI. II. fig. 17). The inner hypoarium on either 

 side, owing to want of space, is smaller than normal, arid lies 

 above and in front of the outer hypoarium. The optic lobes show 

 a remarkable transition between the double and the single con- 

 dition. Their cavity and roof-parts are single, while the basal 

 structures are doubled. There are thus two pairs of 3rd nerves. 



