THE BKAIN. 



375 



irregular hollow outgrowths arise : at a later stage these out- 

 growths become solid, and separate completely from the stalk. 

 In front of the pineal body the roof of the third ventricle, 



Fig. 151.— A median longitudinal, or sagittal section through the head of a 



Rabbit Embryo of the eighteenth day. (Compare Fig. 149 for a surface 

 view of an embryo at a slightly later stage.) x 10. 



BF, cavity <>t" tftalamencephalon, or third ventricle. BH, cavity of medulla 

 oblongata, or fourth ventricle. BL. cerebellum. BH, cavity of mid-brain. BS. cavity 

 of cerebral hemisphere, or lateral ventricle. BT, lamina terminalia. BY, cavity of 

 olfactory lobe. OT, thyroid cartilage. ET, mesethmoid cartilage. P.l, first cervical 

 or atlas vertebra. F.2. second cervical or axis vertebra. IN, infundibulum. LB, 

 trachea. LT. glottis. MC. Meckel's cartilage. NS, central canal of spinal cord. 

 OB, buccal cavity. OI, odontoid process of axis vertebra. OX, supraoccipital 

 cartilage. PP, posterior nan'al chamber. PL, palate. PN, pineal body. PT, 

 pituitary body. BP. basilar plate. TINT, tongue. TO, oesophagus. TP, pharynx. 

 XA. choroid plexus of thinl ventricle. XB. choroid plexus of fourth ventricle. 



which is here excessively thin, becomes thrown into folds, which 

 hang down into the cavity of the ventricle (Fig. 151, xa). Be- 

 tween these folds blood-vessels pass in, from the vascular meso- 



