PHYLUM CHORD ATA 



429 



Bird. When the mandible is 

 depressed, the contraction of the 

 digastric muscle causes a for- 

 ward movement of the lower end 

 of the quadrate, which pushes 

 forwards the maxillo-jugal bar 

 and the palatines and ptery- 

 goids, the latter sliding upon 

 the rostrum. Both the maxillae 

 and the palatines are articulated 

 in front with the premaxilla, and 

 together push it upwards; in 

 this way depression of the lower, 

 produces an automatic raising of 

 the upper, jaw. The great size 

 and strength of both premaxilla 

 and mandible are remarkable, as 

 also is the fact that the orbit is 

 completely surrounded by bone, a 

 backward process of the lacrymal 

 being joined beneath it by a for- 

 ward process of the frontal. 



The mandible contains in the 

 young Bird the six bones on each 

 side characteristic of Reptiles ; 

 the coronary is, however, often 

 absent. As a rule the head of 

 the quadrate articulates with the 

 roof of the tympanic cavity by a 

 single facet in Ratitse.by a double 

 facet in Carinatce. The hyoid 

 always agrees in essential respects with that of the Pigeon ; in the 



Woodpecker the 



posterior cornua 



are curved round 



.- ,^^ , ^^^^^^wH|^^^^ ^he head and at- 



' -> .^n'>;iJ^^^^^HdHM^^^k tached to the skull 



in the neighbour- 

 hood of the right 

 nostril, a very flexi- 

 ble and protrusible 

 tongue being pro- 

 duced. 



The structure of 

 the shoulder-girdle 

 furnishes one of the 

 Pia. ioc7.-skuii uf Ara <-^^^^J^^°^ ^ photograph by ^^^^ fundamental 



Fig. 100().- Anas boschas (Duck). Ventral 

 view of Skull, a. p.f. anterior palatine 

 foramen ; b. o. basiocclpital ; b. pg. basi- 

 pterygoid process ; b. s. basispheiiold ; b. t. 

 basi-temporal ; e. o. exoccipital ; eu. aper- 

 ture of Eustachian tube ; /. m. foramen mag- 

 num; i. c. internal carotid foramen ; j. jugal ; 

 mx maxilla ; mx. p. maxillo-palatine pro- 

 cess ; oc. c. occipital condyle ; pL palatine ; 

 p. n. posterior uares ; px. premaxilla ; q. 

 quadrate; q.j. quadrato-jugal ; v. vomer; 

 JX, X, foramen for nir.th and tenth nerves ; 

 XII, for twelfth nerve. (From Wieders- 

 heim's Vertebrata.) 



