FRONTAL SECTIONS OF THE HEAD, EMBRYO OF 20 MM. 



257 



the lateral ventricles, which extend outward and upward. The walls, H, of the 

 lateral ventricles are much thinner than the walls of the lower part of the fore- 

 brain and are the anlages of the cerebral hemispheres. In the median plane the 

 hemispheres include between themselves a partition, Fx, of mesodermic tissue 



arach, Sk. 



Fx. ec.gl. 



H. 



L.V. 



Fix. 



C.str. 



hy.gl. 



Fig. 148. — Pig, 20 mm. Frontal Section of Head. Series 40, Section 123. 

 arach. Arachnoid zone, art. Lingual arteries. C.str, Corpus striatum, cc.gl, Ectoglia. Fx, Falx cerebri. H, 

 Cerebral hemisphere, hy.gl. Hyoglossal muscle. L, Lens. L. V, Lateral ventricle. Mk, Meckel's 

 cartilage, m.rec.sup, Musculus rectus superior, m.retr.b, Musculus retractor bulbi. m.r.lat, Musculus 

 rectus lateralis [cf. text). Mx.i, Inferior maxillary nerve. Ph, Pharynx. Fix, Plexus choroideus lateralis. 

 Ret, Retina. Sk, Anlage of membranous skull. Ton, Tongue, x. Unidentified structure. X ''^ diams. 



which can at once be identified as the falx. From the base of the falx there ex- 

 tends on each side a fold, Plx, which projects into the cavity of the lateral ventri- 

 cle. This fold contains in its interior a prolongation of the mesodermic tissue of 

 17 



