82 ZOOLOGY. 



19. Hyoid and Ear-bones. Attached just behind the 

 bulla above, and passing round on either side of the throat 

 to meet at the base of the tongue, is a peculiar series of 



small bones con- 

 stituting the hyoid 

 apparatus (fig. 48). 

 This consists of a 

 median bone (" body 

 of hyoid," or basi- 

 hyal), which gives 

 attachment to the 

 muscles of the 

 Fig. 48,-HYoiD OF DOQ. tongue, and two 



Posterior and side views. pairs of projections, 



the horns or comua. 



Each anterior cornu consists of a row of three rod-like 

 bones cerato-, epi- and stylo-hyal, and a fourth smaller 

 one, the tympano-hyal, which is fused to the periotic bone. 

 Each posterior cornu consists of a single thyro-hyal bone, 

 but the pair of thyroid cartilages in the walls of the larynx 

 are really distal portions of this posterior cornu. This 

 peculiar series of bones will be better understood after we 

 have studied lower types of vertebrata. 



Hidden by the bulla, and just external to the periotic 

 bone, are the auditory ossicles, the malleus, incus, os orbicu- 

 lare, and stapes. These will be more explicitly treated 

 when we discuss the ear. 



20. General View of Skull. When we come to the 

 study of the nerves, we shall revert to the skull, and treat 

 of its perforations. The student should not fail, before 

 proceeding, to copy and recopy our figures, and to make 

 himself quite familiar with them, and he should also obtain 

 and handle an actual skull. For all practical purposes the 

 skull of a cat will be quite as useful as that of the dog ; 

 and even that of a sheep or rabbit will show the same 

 bones with various differences of detail. 



The following table presents these bones in something 

 like their relative positions. A closer approximation to 

 the state of the case will be reached if the student will 



