292 AVES. 



and into the sides of the lower jaw from the slender muscle ; it arises from the pterygoid 



articulation as far forward as the commence- process and body of the sphenoid, and is in- 



ment of the horny bill. serted principally into the inner side of the 



In the Cormorant there projects backwards lower jaw and tympanic bone ; it also sends 



from the spine or squamous element of the off a small tendon to the membrane of the 



occipital bone, an osseous style about an inch palate. This muscle draws forward the lower 



in length, of a trihedral figure and tapering to jaw and depresses the upper one. 



a point. It is not anchylosed as a process of In the Cross-bill (Loxia curvirostra) there 



the occiput, but is moveably articulated to it ; is a remarkable want of symmetry in the 



and its description has been referred to this muscles of the jaws on the two sides of the 



section because it does not constitute a regular head corresponding to their peculiar position, 



part of the skeleton, not representing any Those of the side towards which the lower 



essential element of the bony fabric, but is to jaw is drawn in a state of rest (which varies 



be regarded like the bony tendons of the legs in different individuals) are most developed, 



as an ossification of the intermuscular aponeu- and act upon the mandibles with a force that 



rosis of the temporal muscles to which it enables the bird to dislodge the seeds of the 



affords a more extensive and firmer origin, fir-cones, which constitute its food. 



This, indeed, is its essential use,* for the mus- The articulation of the lower jaw is strength- 



cles of the upper part of the neck are inserted ened and its movements restrained by two 



into the occipital bone, and glide beneath the strong ligaments, one of these (a) is extended 



posterior or superadded fasciculi of the tem- from the ligament completing the lower part 



poral muscle. Analogous parts appended to of the orbit, or from the zygomatic process of 



the true spinous processes of the vertebrae are the temporal bone, and is inserted at the outer 



met with abundantly in the inferior vertebrate protuberance near the joint of the lower jaw, 



classes, especially in fishes, where they extend and must prevent the bill from being too 



frequently above the spines of the whole ver- widely opened. The second ligament extends 



tebral column, increasing the surface of origin from the zygomatic process of the temporal bone 



of the lateral series of muscles. directly backwards to the posterior part of the 



The muscle analogous to the Biventer articular depression of the lower jaw, and is 



maxilla (18) arises by two portions, the one designed to guard against the backward dislo- 



from the lateral depression of the occiput, the cation of the lower jaw. 



other from the depression behind and below The muscles of the ribs. The levatores 



the external meatus auditorius ; they are in- cost arum arise from the posterior part of the 



serted into the back part and angle of extremities of the transverse processes, and 



the lower jaw. A similar disposition of converge to be inserted into the anterior 



the digastricus is met with in many of the margin of the succeeding posterior rib. Those 



rnammalia; even in the Orang-utan (Simla of the first and second ribs represent the 



Satyrus) it is equally devoid of a central Scaleni, and are of larger size, arising from 



tendon, and is unconnected with the os hyoides. the last and penultimate cervical vertebrae. 



The openers and closers of the mandibles The Intercostales externi appear to be con- 

 present very slight differences of bulk in rela- tinuations of the Levatores costarum, and are 

 tion to the development of the parts they are usually divided into an anterior and posterior 

 destined to move; their disproportion to the moiety corresponding to the marked separation 

 bill is, on the contrary, truly remarkable in the and moveable articulation between the vertebral 

 Horn-bills, Toucans, and Pelican, and the bill and sternal portions of the ribs ; the anterior 

 is but weakly closed in these in comparison division arises from the costal appendage and 

 with the shorter-billed birds. extends to the anterior extremity of the rib ; 



The upper mandible is moved by three to afford a more advantageous origin to this 



muscles on either side. The first is of a radiated inspiratory muscle would appear, therefore, to 



form, arises from the septum of the orbits, and be one of the uses of the costal appendages, 



converges to be inserted into the external and as well as to strengthen the connection of the 



posterior end of the pterygoid bone, just where ribs to each other. 



this is articulated to the tympanic bone. It The Internal intercostals commence at the 



draws forward the pterygoid bone, which pushes sternal extremities of the ribs, as in mammalia, 



against and raises the upper jaw. but extend backwards no farther than the costal 



The second muscle analogous to the External appendages; their fibres run in an opposite 



Pterygoid arises from the space between the direction to the external intercostals, and are 



posterior part of the orbit and external meatus shorter, the insertion into the posterior suc- 



auditorius, and is inserted intb the internal ceeding rib being by a thin but wide aponeu- 



process and contiguous surface of the tympanic rosis: in the Penguin they are, however, 



bone; it affects the pterygoid process, and con- wholly muscular. Two other layers of inter- 



sequently the upper mandible in the same costal muscles, corresponding to the triangu- 



way as the preceding muscles, and assists in laris sterni, and having the same direction 



opening the bill. of fibres, are extended from before backwards 



The Pterygoidcus Internus is a long and and outwards to the four anterior sternal por- 

 tions of the ribs ; arising from the superior and 



* See- Yarrcll < On the Anatomy of the Cormo- external angle of the sternum, 



ant,' Zoo). Trans, v. iv. p. 235. The muscles of the abdomen are small and 



