46 ANATOMY OF VERTEBRATES. 



The ha3mal arcli of the parietal vertebra, fig. 26, 40, 43, is 

 more reduced than in the Crocodile, and owes much of its appa- 

 rently typical character to the retention of the thyrohyals, 46, 47, 

 borrowed from a branchial arch of the visceral system, which 

 arches are transitorily manifested in the embryo bird. These 

 spurious cornua project freely or are freely suspended. 



The bones, lo (orbitosphenoids), of the third neural arch coa- 

 lesce with each other, and with the centrum below, protect a 

 smaller proportion of the prosencephalon than in the Crocodile, 

 but maintain their neurapophysial relation to it and to the 

 optic nerves, below the exit of which they begin to ossify. The 

 neural spines, ii (frontal), cover a larger proportion of the 

 hemispheres, and, with their homotypes, 7, exhibit a marked 

 increase of developement in conformity with that of the cerebral 

 centres protected by their respective arches. The parapophysis 

 of the frontal vertebra, 12 (postfrontal), is relatively smaller 

 in the Bird than in the cold-blooded Vertebrates, and is rarely 

 ossified from an independent centre, as it is in the Emeu. The 

 hagmal arch of the frontal vertebra, receding from its typical posi- 

 tion as the HcBmatocrya advanced in time and in developement, is 

 now wholly transferred to the parietal one ; its pleurapophysis (28, 

 the ' tympanic '), which is simple, as in the Crocodile, articulates 

 with the parietal parapophysis, 8 (mastoid), though this in some 

 Birds unites with that of the frontal vertebra, 12. The bone, 28, 

 is the chief and most direct osseous developement from the proxi- 

 mal portion of the cartilage of the tympano-mandibular visceral 

 arch : the special appendages of the acoustic organ are developed, 

 as in the Lizards and Snakes (vol. i. fig. 444, b, e), in connection 

 Avith, but not in or from that cartilage. In the young Ostrich 

 and many other birds traces of the composite character of the 

 ha^mapophysis (mandibula) are long extant; and bear obviously 

 a homological relation to the teleologically compound character 

 of the same element in the Crocodile : the pieces, Nos. 29, 29', so' 

 and 31, first coalesce with each other, and then with the haemal 

 spine (32, ' dentary element '), the halves of which are confluent 

 at the symphysis. 



The centrum, (1.3, ' vomer') of the nasal vertebra is single, and 

 usually coalesces Avith the neurapophyses (prefrontals), 14, and 

 pleurapophyses (palatines), 20, of its OAvn segment, and with the 

 rostral production of the frontal centrum, 9 : it is elongated and 

 pointed at its free termination, and deeply grooved above where it 

 receives the above-named rostrum ; indicating both by its form 

 and position that it owes its existence, as bone, to the ossification 



