36 FREDERICK TILNEY AND LUTHER F. WARREN 



comes in contact with the ventrally flexed distal extremity of 

 the parietal eye. The velum transversum is well developed and 

 is plexiform in character, being highly vascular in structure. 

 Following the velum transversum is a dorsal sac usually, how- 

 ever, less conspicuous than the paraphysis and oftentimes smaller 

 than that organ. The commissura habenularis follows and is 

 in connection with two symmetrical ganglia habenulae. A pars 

 intercalaris anterior is not observed. 



The epiphyseal complex has a different arrangement in the 

 several different classes of reptilia. In most Lacertilia the part 

 which seems to be the homologue of the parapineal organ has 

 become converted into a definite parietal eye with lens, retina, 

 and nerve of its own. The pineal organ, on the other hand, is 

 much reduced and appears but a remnant of the homologue of 

 this structure in some of the lower forms. In the orders of 

 reptilia, other than Lacertilia, the parapineal organ does not 

 develop and the pineal organ itself is reduced to a mere rudiment, 

 being represented wholly by the development of its proximal 

 portion. A short pars intercalaris posterior follows the epi- 

 physeal complex while a relatively large posterior commissure 

 forms the caudalmost structure in the roof of the interbrain. 



8. The pineal region in aves 



In birds, only the proximal portion of the pineal organ, the 

 part usually called the epiphysis or corpus pineale, develops. 

 It usually appears as a small circumscribed sac connected with 

 the roof of the interbrain or else it has a definitely glandular 

 structure with acini of varying size. Mihalkovicz 274 in 1874-77 

 studied the epiphysis in Meleagris gallopavo and in this bird 

 called attention to the definite follicular and glandular char- 

 acter of the tissue. Mihalkovicz' description is the most com- 

 plete concerning the epiphysis in birds. Galeotti 140 in 1892 

 added some details to Mihalkovicz' description of this struc- 

 ture and confirmed the opinion that it was glandular in its nature. 

 The pineal region in birds is compressed cephalodorsad because 

 of the marked development of the hemispheres and the cere- 



