THE BEAIN. 



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 Embrj'o of the eighteenth day. (Compare Fig. 149 for a surface 

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



BF, cavity of thaliimeiiuophalou, or third ventricle. BH, cavity of malulla 

 nl)loii,LMt;i. or foiirtli ventricle. BL, cerebelhuu. BM, cavity of mid-braiu. BS, cavity 

 (it rcreiTiil hemisphere, or Literal ventricle. BT, lamina terminalis. BY, cavity of 

 <ilfaetory lobe. CT, thyroid c;irtila^n.\ ET, mesetlimoid cartilage. F.l, first cervical 

 or atlas' vertebra. P. 2. f-oeonil ceri-ical or axis vertebra. I!N", infnndibulum. LE, 

 trachea. LT, glottis. MC. Meclcers cartilage. HS, central canal of spinal cord. 

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

 cartilage. PF, posterior narial cttaujber. PL, palate. PM", pineal body. PT 

 jntuit.T.ry body. RP, basilar plate. TW", tongiie. TO, cesophaglis. TP, pharynx.' 

 XA, choniid plexus of third ventricie. 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- 



