^4) ABNORMAL CONDITIONS OF THE AXIS. 



The corpus callosum is almost always absent, the fornix is ab- 

 sent or rudimentary, the cerebral lobes are usually very defec- 

 tive and are fused in front with each other ; the third and lateral 

 ventricles, in most cases, are opened out into a large cyst, which 

 occupies the greater part of the cranial cavity, a condition which 

 may well induce the belief that the cause of the phenomenon is 

 probably internal hydrocephalus at a very early period of em- 

 bryonic life. It is certain that hydrocephalus often accompanies 

 this condition : examples are seen in specimens Nos. 185 and 186. 



a. Hhinocephalus. 



Syn. Rhmocephalus and Cyclocephalus, Geoff. 

 Cyclops, Gurlt. 



In Rhmocephalus the naso-frontal processes form a frontal 

 proboscis. 



160. A foetal LamVs head with entire deficiency of the axis in 



the facial region, a solid frontal proboscis, partially fused 

 eyes, and a pair of imperfect nostrils between the maxillae. 

 The roof of the skull has been removed to show the com- 

 plete absence of the ethmoid bone and fusion of the optic 

 foramina. Hunterian. 



161. The brain of the same showing the fusion of the hemi- 



spheres in front, the absence of the corpus callosum, the 

 open condition of the large third ventricle, and the com- 

 plete absence of the olfactory nerves. Hunterian. 



162. The head of a foetal Boar, with complete deficiency of the 



facial axis. The eyes are partially fused. An orifice cor- 

 responding to the nostrils is situated at the extremity of 

 the proboscis. Hunterian. 



163. A similar preparation with the eyes more closely united. 



Hunterian. 



164. The head of a foetal Sow, similar to the last two, but with 



the eyes still more closely united. Hunterian. 



165. The head of a foetal Sow, in which the frontal proboscis is 



turned back over the forehead. The eyes are fused as 

 far as the edges of the cornese. 



166. The head of a foetal Pig with the eyes fused into a single 



globe. The roof of the skull has been removed to show 



