50 ANATOMY OF VERTEBEATES. 



and its general homology as a ' neurapophysis ; ' its extent and 

 connections are shown in fig. 8, p. 22, of CXL, and in the speci- 

 men, No. 1363, of XLIV ; it articulates below mth the basi- 

 sphenoid, behind with the mastoid, 8, and petrosal, above wath the 

 parietal, 7, and frontal, n, in front with the orbitosphenoid, lo, 

 combining with it to form the foramen lacerum anterius, through 

 which orbital portions of the fifth nerve pass ; and which usually 

 blends with the common foramina optica, encompassed in great 

 part by the orbitosphenoid. 



The homology of 8, figs. 25, 28, 31, Avith the bone so numbered, 

 and called ' mastoid' in voL i. figs. 75, 81, 91, 92, 93, 95, and 97, 

 is plain ; it forms part of the cavity for the otic capsule, as in 

 Fishes, and part of the tympanic cavity, as in the air-breathing 

 Hsematocrya. As in Reptiles, it offers the articular cavity to 28, 

 a relation partially fulfilled in Fishes ; it sends oiF the second, 

 counting fonvard, of the great outstanding processes for the in- 

 sertion of muscles from the trunk and neck ; it is developed in 

 and from the thick lateral cartilaginous mass of the primordial 

 cranium, connately mth the otic capsule (petrosal). Besides the 

 ^mastoid process,' figs. 27, 29,8, a second so-called 'tympanic 

 process' is developed in some Birds. ^ The articular canity for 

 the bone, 28, is single in Apteryx, Dinornis, Struthio, and a few 

 other birds, but double in most ; in Aptornis there are three 

 articular surfaces.^ The mastoid process varies in shape and size ; 

 in a few birds, as in Calyptorhynchus and Aptornis, it repeats 

 the secondary character more commonly seen in Reptiles by unit- 

 ing with the third cranial diapophysis, 12, and forming an upper 

 zygomatic arch across the temporal fossa.^ The optic foramina 

 indicate the orbitosphenoids, wdiich, like neurapophyses of the 

 trunk, in certain instances, coalesce below and di\ide their seg- 

 ment of the neural axis from the vertebral centrum. In Birds 

 they are uplifted, as in the Perch (vol. i. fig. 85, 10), far above 

 the representative, 9, of their centrum. The divergence of the 

 neural laminaj above the median confluence, to support the pros- 

 encephalon, is Avell shown in CXL. fig. 8, and in the specunen. 

 No. 1363, XLiv., p. 262. In the antecedent neurapophyses, 14, 

 the tendency to median confluence increases, and they become 

 confluent not only below, but above their segment, encompassing 

 the canal, foramen, or foramina, for the olfactory nerves (rhi- 



* Bustard, xviir. vol. iii. p. 352, pi. 52, fig. 9, 8'. ^ lb. p. 352. 



3 lb. p. 352, pi. 52, fig. 1, 8, 12; CXL'. pi. 1, fig. 1, 8, 12. In the memoir above 

 cited this skull is described as belonging probably to X>. Casuarinus, ib. p. 376; 

 it is, however, of D. didiformisy since generically separated as Aptornis. 



