116 



ON THE VERTEBRATE SKULL. 



parts, — an upper, divided into two by a median septum, the 

 nasal passages ; and a lower, the oral cavity . 



The posterior portion of the bisected skull (Fig. 49) presents, 

 in like manner, a strong floor (BO) and a large upper chamber 

 for the lodgment of parts of the brain ; but the lower chamber 

 seems at first to be absent in the skeleton, being represented, 

 in fact, only by the styloid processes (St), the so-called stylo- 

 hyoid ligaments, and the hyoidean bone (Hij) which is suspended 

 by these ligaments to the skull. 



Fig. 49. 



Fig. 49. — The posterior half of the transversely bisected skull, Fig. 48. — B.O., the basi- 

 occipital ; E.O., E.O., the ex-occipitals ; 7', the temporal l>one left in outline ; O.F., 

 occipital foramen; VII., canal for the portio dura and poitio mollis; IX., foramen 

 for the ninth or hypoglossal nerve 



A longitudinal and vertical section of the skull (Fig. 50) 

 enables us to observe the same relations of the parts from 

 another point of view. The central bones (BO, BS, PS, Eth., 

 Vo), which lie between the arches of the brain-case above, and 

 the arches of the face below, are, in such a section, found 1<» 



