MUSCULAR SYSTEM OF AVES. 93 



in the Woodpeckers, where the tail, by means of its stiff and 

 pointed qnill-feathers, serves as a prop to support the bird on the 

 perpendicular trunks of trees on which it seeks its food. In these 

 the ischio-coccygeus, ib. 14, is of large size, extending from the 

 lower edge of the ischiadic tuberosity, and from the diapophyses 

 of the anterior caudal vertebrae to the hajmapophyses of the pos- 

 terior ones, and to the sides of the ploughshare bone. 



Of the Muscles of the head, those which are attached to it for 

 its general motions have already been described ; the remaining 

 muscles of this part are devoted to the movements of the jaws, the 

 tongue, the eye, and the ear. 



The muscles of the jaws are chiefly modified in relation to the 

 moveable condition of the upper mandible and tympanic bone, 

 and the subserviency of the latter to the actions of these parts. 



The temiioralis, fig. 35, 17, fills the temporal fossa, which con- 

 sequently indicates the bulk of that muscle in the dry skull. It 

 arises from a greater or less extent of the temporal and parietal 

 bones, and, as it passes within the zygoma, becomes closely 

 blended with the masseter ; the united muscles derive an acces- 

 sion of fibres from the lower part of the orbit, and are inserted 

 into the raised superior margin, representing the coronoid process ; 

 and into the sides of the lower jaw from the articulation as far 

 forward as the commencement of the horny bill. In the Cormo- 

 rant, the osseous style, moveably articulated to the superoccipital, 

 affords to the temporal muscles a more extensive origin. This, 

 indeed, is its essential use,^ for the muscles of the upper part of 

 the neck are inserted into the occipital bone, and glide beneath 

 the posterior or superadded fasciculi of the temporalis. 



The biventer maxlllce, ib. 18, arises by two portions, the one 

 from the lateral depression, the other from the lower part of the 

 paroccij)ital ; they are inserted into the back part and angle of 

 the lower jaw. 



The openers and closers of the mandibles present very slight 

 differences of bulk in relation to the developement of the parts they 

 are destined to move ; their disproportion to the bill is, on the 

 contrary, truly remarkable in the Horn-bills, Toucans, and Pe- 

 lican, and the bill is but weakly closed in these in comparison 

 with the shorter-billed birds. 



The upper mandible when moveable is acted on by three 

 muscles on either side. The first is of a radiated form, arises, 

 from the septum of the orbits, the fibres converging to be inserted 



> XXIV. p. 234. 



