THE PIGEON 203 



the small forward end the maxillary. Medial to this bar the quad- 

 rate is joined with the premaxilla by a second row of bones, con- 

 sisting of the pterygoid and the palatine, the former articulating 

 with the quadrate, the latter with the premaxilla. 



The lower jaw, or mandible, is a bony arch, composed of five 

 pairs of bones fused together. The hinder end on each side is 

 formed by the articular bone, which articulates with the quad- 

 rate. The articular is an ossification of the proximal end of 

 Meckel's cartilage, which in the embryo forms the whole of the 

 lower jaw. This cartilage persists in the adult, but is covered with 

 membrane bones. These are the dentary, the largest of the bones 

 of the mandible, which forms the anterior half of each side ; the 

 supra-angular, which forms the dorsal portion of the posterior 

 half ; and the angular, a small bone on the inner side of the pos- 

 terior portion. 



Exercise 47. Draw the lateral aspect of the skull on a scale of 2. 



Study the ventral surface of the skull after the lower jaw has 

 been removed. At the hinder end is the basi-occipital, bearing the 

 condyle. Covering the base of the cranium between the tympanic 

 cavities is a large membrane bone, the basitemporal, which repre- 

 sents the posterior portion of the parasphenoid of lower verte- 

 brates. This bone entirely covers the basisphenoid and, in old 

 birds, is fused with it. In front of it is an elongated membrane 

 bone, the rostrum, which represents the anterior portion of the 

 parasphenoid. It covers and is fused with the presphenoid, mes- 

 ethmoid, and orbitosphenoids. 



The upper jaw will be seen to be composed of two paired rows 

 of bones, an outer and an inner one, which meet on each side, 

 at the quadrate bone posteriorly and at the premaxilla anteriorly. 

 The outer row is composed of the maxillae, the jugals, and the 

 quadratojugals ; the inner row, of the pterygoids and the palatines. 

 The pterygoid is a short bone, articulating with the inner surface 

 of the quadrate and with the rostrum. The palatine is a long bone, 

 extending forward from the pterygoid, its hinder portion being 

 broad, its anterior portion slender. Note carefully the relation 

 of all these bones to one another. 



