CYCLOPIA IN THE HUMAN K.MHKVD. 21 



internal forms of the brain. These illustrations are given in the His monograph 

 as figures 2 and 33, and they are also copied by Streeter in his article on the brain 

 in the Manual. It may be stated that figure 33 shows the neuropore nearly 

 closed, the optic stalk being still represented as a wide-open canal which reaches 

 to the midventral line. Dorsal to the optic stem is a slightly marked pocket 

 which reaches to the neuropore, and it is believed by His that this represents the 

 beginning of the cerebral hemisphere. It is interesting to note that Keibel and 

 Else state in their Normal Plates (page 100) that the cerebral vesicles are just 

 beginning in embryos 4.5 to 5 mm. long. It may be that His exaggerates this 

 pocket slightly in his model, but it is of great value to us to have his opinion regard- 

 ing the location of the primordia of the cerebral hemispheres in the brain-tube 

 before the neuropore is closed. According to Watt, the cerebral hemispheres 

 arise much more dorsal than is indicated by His in his figures. 



Keibel and Else give excellent illustrations of the form of the brain up to the 

 time of the closure of the neural tube. No doubt the Kroemer-Pfannenstiel 

 embryo, which contains five or six myotomes, represents a normal stage with 

 medullary plates wide open, and in this embryo there is no indication whatever 

 of an eye primordium. The same is true in the Kollmann embryo, containing 14 

 myotomes, which is illustrated by Keibel and Else as figure 4. This specimen 

 also seems to me to represent a normal embryo, as we have in our collection a 

 stage that is practically identical with it. Our embryo No. 391 contains seven 

 pairs of somites, and has been carefully studied and published by Dandy. A 

 model of it, as well as sections through the head, has also been pictured by Evans 

 in figures 408 and 409, Volume II, of the Manual, and it shows no out-pocketings 

 in the anterior part of the brain to represent the eye primordia. However, when 

 we reach Keibel and Else's figure 5, which is taken from the Pfannenstiel III 

 embryo, two marked diverticula are seen to arise from the front end of the neural 

 tube, which Keibel, in his article on the eye in the Manual of Embryology, believes 

 to represent the primordia of the eye. 



As Keibel and Else have reproduced numerous figures of sections through 

 the head of this embryo, it is easy to ascertain the exact form of its neural tube. 

 However, I am of the opinion that we can hardly view the neural tube in this 

 embryo as normal, as it is not sufficiently advanced in development for an embryo 

 of this stage and as it corresponds very much in form with the brain of our embryo 

 No. 12, which I believe to be pathological. At this time the neural tube should 

 be nearly closed, while in Keibel and Else's specimen and in our No. 12 it is still 

 wide open. The Pfannenstiel III embryo contains the same number of somites 

 that is, 14 as our embryo No. 12, and the form of the brain and of the eye-vesicles 

 is very similar in both embryos. A picture of the external form of embryo No. 12 

 will be found in my article on the development of the intestines (plate 19, fig. 2) . 

 My reason for believing that the brain form in both of these embryos can not be 

 viewed as normal is that in other young specimens published recently by Wallin 

 and by Bremer quite a different form of the brain-tube is shown for this stage 

 of development. The Wallin specimen, which contains 13 somites, has the brain- 



