98 ELEMENTAR Y ANA TOMY. [LESS. 



The hinder end of the basi-occipital has a more important 

 function in the Sauropsida than in man's class, as it develops 

 a convex projecting head or condyle, which articulates with 

 the vertebral column. In most Fishes it is concave, its con- 

 cavity being applied to the concavity of the body of the first 

 vertebra in the same way that all the bi-concave vertebrae arc 

 united together. 



FIG. 95. VERTICAL, LONGITUDINAL SECTION OF THE SKULL OF A FOWL. 

 {After Parker.} 



a, angular bone of mandible ; as, alisphenoid ; az, articular bone of mandible : 

 bo, basi-occipital ; d, dentary bone of mandible ; f, frontal ; me, median 

 ethmoid ; os, orbito-sphenoid ; /, parietal ; /', pro-otic ; pf, pituitary fossa ; 

 px, pre-maxilla ; sa, surangular bone of the mandible ; so, supra-occipital ; 

 sp, splenial bone of the mandible ; sg, squamous part of the temporal bone, 

 or squamosal ; v, vomer. 



The lateral parts (exoccipitals] are constantly ossified where- 

 ever the skull is ossified at all ; and their position with 

 regard to the spinal marrow is constant. They always 

 transmit, either as in man by a notch, or by a foramen, the 

 eighth pair of nerves, and also the hypoglossal nerve where it 

 exists, but this latter is wanting in Fishes. 



In the fact that the occipital condyles are mainly formed 

 by the lateral parts (exoccipitals), man agrees with his own 

 class. They may, however, be entirely formed by the ex- 

 occipitals, as in Batrachians ; or these bones may more or 

 less help to form one single median convex articular condyle, 

 as in the Sauropsida. 



The peculiarities as to the position of the foramen magnum 

 will be spoken of in considering the skull as a whole. 



The Squama of man, or supra-occipital, is of a relative 

 size greatly in excess of that which exists in most forms, but 

 still it may attain a yet greater importance than in him. This 

 is the case, for example, in the Cetacea and in the Elephant, 

 where its relative as well as absolute size is enormous. 



