SKELETON 



105 



the skull so that the axis of the skull is at right angles to that of the body. There 

 is only a single temporal fossa, bounded laterally by an arcade of zygomatic and 

 quadratojugal, connecting quadrate and maxillary. There is a preorbital 

 vacuity; and the nares may have the posterior margin rounded (holorhinal) or 



slit-like (schizorhinal). The premaxillaries 

 are fused and sclerotic bones are common. 



A peculiarity of the ventral surface is the 

 union of the anterior part of the parasphenoid 

 to the basisphenoid to form a 'rostrum sphe- 

 noidale' which projects forward in the middle 

 line. The rest of the parasphenoid forms a 

 'basitemporal plate' below the basisphenoid 

 and basioccipital. Dorsal to the rostrum is a 

 small presphenoid (sometimes lacking in the 

 adult) to which the orbitosphenoids are at- 



FlG. 110. — Ventral view of skull 

 of a duck; bt, basitemporal plate; 

 ch, choana; eo, exoccipital; j, zygo- 

 matic (jugal); mx, maxillary; p, 

 palatine; pmx, premaxillary; pt, 

 pterygoid; q, quadrate; qj, quad- 

 ratojugal; r, rostrum; v, vomer. 



Fig. III. — Hyoid of hen, after Parker. 

 e, entoglossal; p, paraglossal; «, urohyai; 

 ///, posterior cornua. 



tached as ala:, while the alisphenoids become similar wings to the basisphe- 

 noid. Ectethmoids are connected with the mesclhmoid; they are some- 

 times large, appearing ('prefrontals') on the top of the skull. Epi- and ecto- 

 pterygoids are lacking. The pterygoids, here membrane bones, extend 

 from the quadrates to the palatines, and the two either slide along the rostrum 

 or the vomers intervene. This, together with the hinging of the front part of 

 the skull upon the rest, forms a mechanism by which the upper jaw is raised 



