CEREBRAL VENTRICLES IN THE PIG 223 



The oldest embryo studied measured 260 mm. Its brain was 

 dissected out, embedded in celloidin, and cut into sections 0.2 mm. 

 thick. From these sections a wax model of the ventricles was 

 constructed, as shown in figures 25 and 26. The three subdivi- 

 sions of the lateral ventricle have become highly developed. 

 The anterior horn, which in the 45-mm. embryo ended in a short 

 and slightly pedunculated olfactory bulb, now extends through 

 the olfactory stalk and terminates in the expanded ventricle of 

 the olfactory bulb. The body of the lateral ventricle is corru- 

 gated above, w^here it is in relation with bundles of fibers in the 

 corpus callosum. The inferior horn not only descends, but ex- 

 tends forward as a slender prolongation, which ends blindly in the 

 temporal lobe of the brain. As seen from below, the cast of the 

 lateral ventricle shows the concavities for the corpus striatum and 

 the hippocampus respectively, separated by a ridge into which 

 the chorioid plexus is invaginated. The ridges bounding the cor- 

 pus striatum correspond with those seen in the 45-mm. embryo. 



In the 260-mm. specimen, the interventricular foramen has 

 expanded considerably, and its area was found to be 6.92 sq. 

 mm. Extending backward from the foramen, between the region 

 occupied by the thalamus below and the tela chorioidea above, 

 there is a tubular expansion of the third ventricle, somewhat 

 flattened dorso-ventrally. This corresponds with the much 

 smaller expansion, T-shaped in section, which was described in 

 the 45-inm. embryo. In the 260-mm. embryo there is a long 

 caudal extension of the dorsal part of the third ventricle which 

 curves slightly upward and forms the suprapineal recess. It 

 measures about 5.6 mm. in length and extends backward with 

 quite a uniform diameter of 1.4 mm. This conspicuous feature 

 is not represented in the 45-mm. specimen. The cast of the cav- 

 ity (fig. 25) is deeply corrugated on all sides by longitudinal folds. 

 These accomodate branches of the medial cerebral vein. A large 

 branch of the vein on either side produces a deep groove along 

 the dorsal expansion of the third ventricle. Between the su- 

 prapineal recess above and the pineal recess below there is a well 

 marked lateral compression of the ventricle, produced by the hab- 



