SKULL MAMMALS 



20I 



the larger. When fully developed the hyoid cornu consists of four 

 elements, usually called, beginning below, hypo-, cerato-, stylo- 

 and tympanohyals, the dorsal element contributing to the stapes. 

 (It has not been shown that hypo- and ceratohyal are the 

 homologues of the elements with the same name in lower Verte- 

 brates.) The tympanohyal may ankylose with the petrosal, 

 and, fused with the stylohyal, forms the styloid process. In other 

 cases the connexion with the stylohyal may be ligamentary, and 

 when, as in man the ceratohyal fails to ossify, a stylohyal Ugament 

 extends to the hypohyal (lesser cornu). The second horn which is 



(A) m 



Fig. 209. — A, Hyoid of horse (St. Hilaire); B, ventral and side views of Monotreme 

 larynx (Gegenbaur, '98). b, basihyal; c, ceratohyal; cr, cricoid; e, epihyal; g, glosso- 

 hyal; h, hyoid arch; 5, stylohyal; /. thyreoid cartilage; th, thyreohyal; tr, upper part of 

 trachea. 



usually coossitied with the body, has no connexion with the cranium, 

 but is connected by ligament with the thyreoid cartilage of the larynx. 

 It never contains more than one article. 



Ossicula Auditus. — The mammahan ear bones furnish one of the 

 problems around which there is an extensive Hterature. It has been 

 possible to settle with some degree of certainty the homologies of 

 these elements, but as yet paleontology has not confirmed the con- 

 clusions of comparative anatomy and embryology. 



There are three bones in the mammalian middle ear (p. 119) 

 between the fenestra vestibuli (ovale) and the tympanic membrane: a 

 stapes, stirrup-shaped and perforated for the stapedial artery, its base 

 lying in the fenestra, while distally it articulates with the second 



