128 MB. "W. K. PARKER ON THE STRUCTURE AND 



figs. 3, 4, 5, s.n. r.h.s. v.). Further forwards, the septum gently narrows to the middle, 

 and then thickens again towards the base, the sectional view of which is always bulbous 

 (Plate X. fig. 5). The alse nasi grow forwards beyond their aocial attachment ; between 

 them runs the evanescent premaxillary axis, which is flattened from above downwards 

 (Plate X. fig. 6). There is no such outgrowing of the base of the septum as is to be 

 seen in the embryo Ox, in the Crocodile, and in the Frog ; yet such an inferior expan- 

 sion is to be seen in many birds, especially the Raptores. In the Turtle (Chelone mydas) 

 the alee nasi and the base of the septum become confluent at one point. 



Rhea. 



My illustrations of the development of the skull' of the Bhea will be from a com- 

 parison of the adult skull with that of the ripe pullus. I have already given figures of 

 the adult Bhea americana, Zool. Trans, vol. v. pi. 42 ; and there are several notices of 

 its structure in that paper, more especially as compared with that of the Syrrhaptes 

 and the Tinamou. The ripe chicks of the Rhea from the Gardens of the Zoological 

 Society were of a mixed kind ; the sire being the subspecies (1) called B. macrorhyncha 

 by Dr. ScLATER (Zool. Trans, vol. iv. pt. 8. pi. 69, & fig. 2. p. 356 ; & P.Z.S. 1860, p. 207), 

 whilst the dam was the ordinary B. americana. In some respects the Bhea comes much 

 nearer the ordinary land birds, e. g. Otis, Galhis, than the African Ostrich ; in others 

 it is much more aberrant from the ornithic type. It is also the best bird in the Class 

 for illustrating the structure of the Fish, and the lower kinds of Reptilia — the Amphi- 

 bians, Ophidians, and Lacertians. Notwithstanding the large size of these pulli, the 

 cartilage-bones have not all appeared, but the membrane-bones have attained to a 

 degree of development almost equal to that which is found in an ordinary adult Lacer- 

 tian. The condition, moreover, of the primordial (larval) skull is such as wlQ have to 

 undergo great changes of relative proportion, and of subsequent resorption in certain 

 tracts, before it reaches its adult condition. 



A chink in the upper aspect of the oval basioccipital shows a feeble remnant of the 

 notochord in its axis (Plate IX. fig. 1, b.o..) ; the bone itself is insulated by cartilage. 

 The exoccipitals are large, hourglass-shaped within (Plate IX. fig. 1, e.o.), and trilobate 

 at the external and outer margin (Plate IX. fig. 6, e.o.) ; a notch above, near the 

 crescentic venous groove, shows that a large peninsula of this bone (above) belongs to 

 the opisthotic (op.), which is still distinct within (Plate X. fig. 7, op.): this is exactly 

 like what we see in the ripe embryo of the Crocodile. The occipital condyle is bilo- 

 bate transversely (Plate IX. fig. 1), as is very common in birds having a smack of the 

 reptile in them ; it is still cartilaginous, but the ex- and basi-occipitals are creeping into 

 it at its sides and in front. The superoccipital (Plate IX. fig. 6, s.o.) shows no trace of 

 suture down its middle (although assuredly it did once exist, if analogy is of any value); 

 it is a large, elegant, six-sided, winged bone, angular above, crescentic below, grooved 

 and perforated for veins submarginally, and has the upper part of its sides convex, the 

 lower concave. This bone has a large margin of cartilage on each side of it ; it has, 



