ANATOMY OF VERTEBRATES. 97 



the neurapophysis, ' alisphenold,' 6 ; the neural spine, ' parietal,' 

 7 ; and the diapophysis, ' mastoid,' 8. The alisplienoids protect 

 the sides of the optic lobes, and the 

 rest of the penultimate segment of 

 the brain called ' mesencephalon ; ' 

 the mastoids project outward and 

 backward as strong transverse pro- 

 cesses, and giii'e attachment to the 

 piers of the great inverted haemal 

 arch. Before noticing its struc- 

 ture, I may remark that, in the 

 recent Cod-fish, the case, partly 



gristly, l)artly bony, Avhicll contains Dlsartlcnlalcclmescncciilialicmcli.riewed 



, • ^ •'-.,•'. . from litliilid ; Cod aionhua i-nbjaris) 



the organ ol hearmg, is wedged 



between the last and penultimate neural arches of the skull. 

 The extent to which tJie ear-case is ossified varies in different 

 fishes, but the bone is always developed in the outer-wall of tlie 

 case. In the Cod it is unusually large, and is called ' petrosal,' 

 fig. 81, 16; in the Perch, fig. 84, 16, and Carp, fig. 83, lo, it is 

 smaller : it forms iw part of the segmented neuroskeleton. In the 

 acoustic organ whicli it contributes to enclose, there is a body as 

 hard as shell, like half a split almond : it is the ' otolite,' fig. 

 81, 16. 



The ha?mal arch consists of a pleurapopliysis and a ha;mapo- 

 physis on each side, and a hasmal spine ; the pleurapopliysis is in 

 two jjarts, the upper one called ' stylohj'al,' i)3. 38 ; the lower one 

 called ' epihyal," ib. 39 ; the hjemapophj-sis is called ' ceratohyal,' 

 ib. 40. The lia3mal spine is subdivided into four stumpy bones, 

 called collectively 'basihyal,' ib. 4i ; and wliich, in most fishes, 

 supj^ort a bone directed forward, entering the substance of the 

 tongue, called ' glossohyal,' ib. 42 ; and another bone directed 

 backward, called ' urohyal,' ib. 43. 



The ceratohyal part of the hsemapophysis supports an appendage, 

 or rudimental limb, called ' branchiostegal,' fig. 81, 44, answering 

 to the pectoral fin diverging from the haimal arch, in the adjoining 

 occipital segment. 



The penultimate segment of the skull above described is called 

 the ' parietal vertebra ; ' the neural arch is called ' mesencephalic ; ' 

 and the hajmal arch is called ' hyoidean ' in reference to its sup- 

 porting and subserving the movements of the tongue. 



The next segment, or the second of the skull, counting back- 

 ward, can be detached from the foremost segment without dividing 

 any bone. It is then seen to consist, like the third and fourth 



VOL. I. H 



