1890.] On the Anatomy and Development of Apteryx. 455 



wing with hypertrophied second and partially atrophied first and 

 third digits. 



The nostril has acquired its final position at the end of the beak in 

 stage E ; np to the middle of incubation the whole respiratory region 

 of the olfactory chamber, from the anterior nares to the commence- 

 ment of the turbinals, is filled with a solid mass of epithelial cells, 

 through which a passage is formed at a later period. 



At no stage is there any trace of the caruncle or " egg-breaker" at 

 the end of the beak. 



The Law of Growth. — -A number of details are given with respect 

 to the various proportions of the different parts at different ages. 



The Specific and Sexual differences observable in the three species are 

 described. 



The Skull. — In stages A and B the only cranial rudiments present 

 are the parachordal plates, continued cephalad into the prochordal 

 plate, and the visceral arches. 



In stage C the trabecule have appeared, and are continuous with 

 the parachordals ^ the prochordal plate sends off paired processes 

 directly upwards in the mesencephalic flexure and laterad of the 

 third nerves. 



In stages E and E the pituitary fossa is pierced by three apertures 

 in longitudinal series — the anterior, middle, and posterior basi- 

 cranial fontanelles. The middle fontanelle has disappeared in stage 

 O, but the anterior and posterior are still recognisable in stages H 

 and I. Through the anterior fontanelle the pituitary radicle passes. 



The medio-dorsal portion of the dorsum sellse arises as a distinct 

 chondrite, the prochordal cartilage, which in stages E and Gr is quite 

 separate both frorr the trabecular and from the parachordal regions of 

 the skull. 



None of the stages show a separate prenasal cartilage or inter- 

 trabecular ; if present as a distinct chondrite it certainly does not 

 extend further backwards than the anterior presphenoidal region ; the 

 posterior presphenoidal region is clearly formed from the trabecule. 



In stages D, E, and F the presphenoid is a vertical plate of con- 

 siderable antero-posterior extent, and gives origin to a pair of large 

 orbitosphenoids. In stage A the orbitosphenoids have begun to 

 atrophy, and in later stages are reduced to narrow bars of cartilage, 

 the presphenoid at the same time undergoing a great diminution in 

 antero-posterior extent. 



The olfactory capsules extend backwards to the optic foramina 

 mesiad of the eyes ; there is at no stage an interorbital septum. 



The turbinals are unusually well developed, and are divisible into 

 anterior, middle, posterior, anterior accessory, ventral accessory, and 

 mesoturbinal folds. Alone amongst these, the anterior accessory turbinal 

 is formed as a hollow invagination of the wall of the olfactory capsule, 



