THE PIGEON 201 



basi-occipital, beneath and in front of the foramen magnum ; the 

 paired exoccipitals,at the sides ; and the supra-occipital, dorsal toit. 



A more or less prominent semicircular ridge, called the lamb- 

 doidal crest, in which certain muscles of the neck are inserted, 

 runs across the hinder end of the skull, separating the occipital 

 from the parietal region ; at each end of this crest is the tym- 

 panic cavity. 



Study the dorsal surface of the skull. Its roof is formed by 

 three pairs of large membrane bones,— the parietals, frontals, and 

 nasals. The parietals are the hindermost, the suture between 

 them and the frontals being in the young bird at the hinder border 

 of the orbit. The frontals form the portion of the roof between 

 the orbits, the suture between them and the nasals being at the 

 forward border of the orbits. The nasals extend forward from the 

 anterior end of the frontals and form the base of the beak; 

 each one of them sends a long process along each side of one of 

 the nostrils. 



In front of the nasals are the premaxillae, which form the ante- 

 rior portion of the beak and belong to the visceral skeleton. Each 

 premaxilla is composed of three parts, which meet in the tip of 

 the beak : the nasal process and maxillary process, which lie on 

 the inner and outer side of the nasal opening respectively, and the 

 small palatine process, which forms the anterior part of the roof 

 of the mouth. 



Exercise 45. Draw the posterior aspect of the skull on a scale of 2. 

 Exercise 46. Draw the dorsal aspect of the skull. 



Study the lateral surface of the skull. Note the very large orbit. 

 In the hinder part of the skull will be seen the lambdoidal ridge 

 and the tympanic cavity. Between this cavity and the parietal 

 on each side is the large squamosal bone, which forms the posterior 

 border of the orbit. 



The tympanic cavity is a circular depression, within the margin 

 of which is the tympanic membrane, or eardrum. On the inner 

 wall of the cavity are two foramina, the fenestra ovalis and the 

 fenestra rotunda, the former of which is dorsal to the latter and 

 is closed by the stapes, the innermost of the two ear ossicles. The 



