ARREST OF DEVELOPMENT. 55 



only bone in the cranial axis, and it ends in a point in 

 front. 



217. The anterior half of a nanocephalous foetal Kitten. The ex- 



ternal ears were united at the base ; but the left lateral 

 half of the head has been removed to show the head in 

 section. A bristle marks the external opening of the 

 alimentary and respiratory tracts. 



218. A microcephalous Human foetus,in which the face is entirely 



wanting, its position being occupied by a pair of ill-formed 

 ears fused together above and below, with a small rounded 

 tubercle between them in the place of a meatus. The 

 skull and spinal canal have been laid open from behied. 



219. -A longitudinal vertical section of the anterior part of a 



nanocephalous foetal Lamb. The brain in front of the 

 medulla is represented by a cyst only. The pharynx 

 opens externally through the united tympanic bullse and 

 external meatus. Presented by Sir W. Blizard. 



220. The atlas and bones of the skull from the other lateral 



half of the same. The anterior part of the skull is seen 

 to be extremely defective. The bones of the ear-capsule 

 retain their normal position, but the tympanic and squa- 

 mous elements were united across the mesial line in front 

 of the defective cranial axis. 



Presented by Sir W. Blizard. 



221. The left half of a longitudinal section of the anterior part 



of a nanocephalous foetal Pig. The cranial bones are very 

 thick. The specimen is in other respects similar to the 

 last. Hunterian. 



222. The right half of the same. Hunterian. 



c. AcepJialus. 



223. A portion of the spinal column and cord of a foetal Lamb. 



The medulla ends in a rounded extremity. It is sur- 

 rounded by a case, partly of membrane and partly of carti- 

 lage, which represents the cranium : a pair of imperfect 

 periotic capsules are imbedded in its walls. Hunterian. 



224. The anterior extremity of a nanocephalous foetal Lamb. The 



head is represented by a pair of ears and an elongated 

 bladder-like cyst, which projects between and above 



