X SKULL 479 



leaves the skull.' Between the mastoid portion of the periotic and the 

 posterior border of the tympanic, at the juncture of the tubular and 

 bulbous portions of the latter bone, is a small aperture — the stylomastoid 

 foramen — which transmits the seventh nerve ; it and the eighth (VII, 

 VIII) enter the periotic just below the depression for the flocculus of the 

 cerebellum (fl). A space (IX, X, XI) between the occipital condyle and 

 tympanic bulla gives exit to the ninth and tenth, as well as to the 

 eleventh nerve — which is not represented in the dogfish and frog ; and 

 the hypoglossal, which in mammals is counted as the twelfth cerebral 

 nerve, passes out through two small apertures (XII) in the exoccipital, 

 just anterior to the condyle. Various other apertures will be noticed in 

 the skull and jaws : through some of these branches of certain of the 

 above-mentioned nerves pass, while others transmit blood-vessels. 



The lower jaw or mandible (Fig. 122 a) con.sists of two 

 halves or rami, each corresponding essentially to the dentary 

 of the frog, which unite with one another in front, at the 

 symphysis, by a rough surface, while behind they diverge 

 like the limbs of the letter V. Each ramus is a vertical plate 

 of bone, broad behind and tapering towards the front, where 

 it bears the incisor teeth ; further back, on its upper margin, 

 are the sockets for the cheek-teeth, and behind them is an 

 ascending portion which bears the condyle {cor) for articula- 

 tion with the facet on the squamosal ; in front of the condyle 

 is a curved coronoid process. The postero-inferior border, 

 which is rounded and inflected, is known as the angular 

 process (ang. pro). 



The hyoid is a small bone situated at the root of the 

 tongue, anterior to the larynx (Fig. 125 hy). It consists of 

 a stout body or basi-hyal, a pair of small anterior horns, 

 representing the ventral ends of the hyoid arch of lower 

 Vertebrates, and a pair of longer, backwardly-projecting pos- 



1 In most mammals {e.g. dog, cat), the maxillary division of the 

 trigeminal passes out through a separate foramen, behind the 

 sphenoidal fissure ; and the anterior part of the space referred to above 

 is separated off as is a distinct foramen for the mandibular division. 



