xxiv] 



SKULL 



617 



basitemporal, a relic of the parasphenoid of Fishes and Amphibians. 

 In some Reptiles traces of the front part of this bone remain, but 

 in no living Reptile does any trace of the hinder portion of the 

 bone persist, and this is an indication that Birds are descended 

 from a type of Reptile more primitive in some respects than any 

 now existing. Other points of resemblance to Reptiles are that 

 the lower jaw is ensheathed by five dermal bones and has its 

 proximal end replaced by a cartilage bone, the articular ; and that 

 instead of there being a direct hinging or articulation of the 

 lower jaw to the skull, a bone called the quadrate is interposed, 



FIG. 308. Brain of Pigeon, Columba livia x about 2. 



1. Olfactory lobes. 2. Cerebral hemispheres. 3. Pineal gland. 4. Optic 

 lobes. 4 a. Optic chiasma. 5. Cerebellum. 6. Lateral lobe of 

 cerebellum. n. Optic nerves. in. Motor oculi. iv. Patheticus. 

 v. Trigeminal. vi. Abducens. vn. Facial. vm. Auditory, 

 ix. Glossopharyngeal. z. Vagus. xi. Spinal accessory. 



xn. Hypoglossal. 



as in Reptiles, which articulates on the one hand with the lower 

 jaw and on the other with the skull. This quadrate bone is movable, 

 and to it in front are jointed the bones of the palate, the pterygoids 

 and palatines, which slide on, but are not fixed to, the base of the 

 skull. Hence when the lower jaw is opened, i.e. pulled down, these 

 bones are pushed forward, and the upper beak, to which they are 

 fastened in front, is slightly tilted up, thus increasing the width of 

 the gape. In parrots the front part of the skull, including the bones 

 of the face, has an actual joint with the hinder part of the skull. 

 Thus it follows that in spite of the presence of a quadratojugal 



