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MANUAL OF ELEMENTARY ZOOLOGY 



represents that part of the visceral skeleton which does 

 not form the jaws and ear ossicles. It consists of a 



median body, representing the 

 basihyal, and two pairs of 

 backwardly projecting cornua, 

 of which the hinder are the 

 larger. The anterior cornua 

 represent the hyoid arches, 

 and are completed by a 

 series of small separate 

 bones, which connect the 

 hyoid bone with the periotic 

 region of the skull. The 

 posterior cornua represent 

 the first pair of branchial 

 arches. 



The following openings exist in 

 the wall of each side of the skull : 

 (i) The anterior nares at the front 

 end of the nasal capsule, for the 

 nostril. (2) The anterior and (3) 

 the posterior palatine foramina, a 

 large and a small opening in the 

 palate for the passage of branches 

 of the maxillary nerve and blood 

 vessels between the palate and the 

 nasal cavity. (4) The laciymal 

 foramen between the lacrymal and 

 maxillary bones, for the lacrymal 

 duct which conveys tears into the 

 nose. (5) The infraorbital foramen 

 in front of the zygomatic process of 

 the maxilla, for the passage of a 

 branch of the maxillary nerve from 

 the orbit to the face. (6) The 

 optic foramen, a large round hole 

 in the orbitosphenoid for the 

 optic nerve. (7) The foramen 

 lacerum anterius or sphenoidal 

 fissure, a vertical slit between 

 the basisphenoid and alisphenoids 

 for the third, fourth, sixth, and 

 ophthalmic and maxillary branches 

 of the fifth nerves. In most 

 mammals the last-named branch 



Fig. 316. — A diagram of the 

 jaws of vertebrate animals. 



A, The arrangement in the dogfish, in 

 which the hyomandibular takes 

 part in the suspension of the lower 

 jaw {hyostylic) ; B, the arrange- 

 ment in the frog, in which the jaw 

 is suspended by the quadrate 

 {aulostylic) ; C, the arrangement 

 in the rabbit, in which the lower 

 jaw is suspended by the squamosal. 



c, Cranium; /*., hyomandibular; lig., 

 ligaments ; m., lower jaw ; p., 

 palatine;/?., palatoquadrate bar; 

 j>t., pterygoid; q. t quadrate; £?., 

 one of the ear ossicles, possibly 

 representing the quadrate ; sq., 

 squamosal. 



In most fishes the jaws are hyostylic ; 

 in amphibians, reptiles, and birds they 

 are autostylic. 



