THE PINEAL BODY 



47 



The sac is hollow and in communication with the ventricle by 

 means of a slender, hollow stalk. A proximal portion may now 

 be distinguished so that all three elements of the pineal organ are 

 present. The habenular ganglion is recognizable at this stage 

 as a marked thickening in the roof-plate cephalad of the pineal 

 organ. The paraphysis and velum have increased in promi- 



24 



42 



4fl 



18 ^- f-T 2 



3332 



Fig. 14 Mesial view of forebrain reconstruction of 70 mm. Mustelus. X 50. 

 The unshaded area shows the cut surfaces of the reconstruction. According to 

 Tilney, 1915 



2, chiasmatic process; 3, cerebellum; 4, chiasm; 7, epiphysis; 18, infundibular 

 evagination; 24, midbrain; 26, mammillary recess; 27, mammillary body (poste- 

 rior lobe) ; 32, post-chiasmatic eminence (inferior lobe) ; 33, post-chiasmatic 

 recess (recess of inferior lobe) ; 35, post-infundibular recess; 36, post-infundibular 

 eminence; 39. paraphysis; 40, recess of infundibular process; 41, supra-optic crest; 

 42, supra-optic recess; 44, telencephalon ; 47. velum transversum. 



nence. The brains of the 100 mm. and 300 mm. Mustelus 

 approximate the adult conditions shown in figures 15, 16 and 17. 

 Here, with one exception, i.e., the parapineal organ, all of the 

 elements in the pineal region may be identified, including the 

 two parts of the paraphyseal arch, the velum transversum, a 

 short dorsal sac, a massive habenular commissure and habenular 



