70 THE CAT. [CHAP. in. 



by two foramina. The hinder and outer of these, which, is the 

 larger, is the foramen or ah (9), and transmits the third division of 

 the fifth nerve. Immediately in front of this is a smaller opening, 

 the foramen rotundum (8), which transmits the second division of 

 the fifth, nerve. Immediately in front of this again is a large and 

 deep notch which, in the complete skull, is hounded in front by the 

 hinder margin of the anterior sphenoid, and so is converted into a 

 foramen. This aperture is called the sphenoidal fissure. It transmits 

 the first division of the fifth nerve, together with the nerves of the 

 orbit to be hereafter described. The upper surface of the posterior 

 sphenoid exhibits, on each side of the sella, a faintly-marked groove 

 (for a cranial artery) ending posteriorly in a notch. The piece of 

 bone immediately external to such groove and notch, (between the 

 basi-sphenoid and the greater part of the ali-sphenoid) is called the 

 lingula sphenoidalis, and is at one time of life distinct. 



Extending forwards much in front of the basi or ali-sphenoids 

 are two complex bony plates which extend forwards and downwards 

 from the junction of the basi- and ali-sphenoid on each side, and also 

 join the palatine bones in front. Each of these is termed a pterygoid 

 plate (pt) and its flattened upper surface articulates with the under 

 surface of the anterior sphenoid. The under surface of this flattened 

 part forms part of the basis cranii, and towards its outer margin a 

 lamellar process of bone projects downwards, having at its hinder 

 end a curved sharp-pointed process (the hamular process] arching 

 backwards and somewhat downwards and outwards. Externally 

 to this hamular process, the pterygoid plate sends outwards another 

 small, more or less lamellar process. The very small space in- 

 cluded between this last and the hamular process, is called the 

 pterygoid fossa (pf), and there is of course one on each, side of 

 the skull. The very considerable space included between the two 

 pterygoid plates is called the meso-pterygoid fossa, and that is single 

 and median. The part which, immediately supports and forms each 

 hamular process, is originally a distinct bone, called the pterygoid bone. 



The anterior sphenoid is much longer in proportion to its width than 

 is the posterior, but like it consists of a median part with, two wings 

 or lateral expansions. The median part, called the pre-sphenoid (ps), 

 joins the basi-sphenoid behind. It is not solid, but contains a great 

 air-cavity, divided by a median septum into two " sphenoidal sinuses " 

 which open widely at their anterior end (the bone expanding 

 anteriorly into two ethmoidal processes (p) ), to embrace the lower 

 posterior angle of the ethmoid. The pre-srjhenoid bears a median 

 inferior ridge, the rostrum (r) } which is visible between the inner 

 margins of the two pterygoid plates of the posterior sphenoid. The 

 upper surface of the vomer is attached to the anterior part of the 

 rostrum. The upper surface of the pre-sphenoid is much, elongated. 

 Its anterior two thirds support the olfactory lobes of the brain and 

 are convex from before backwards, but slightly concave from side to 

 side. Its posterior third (separated from the more anterior part by 

 two foramina) is slightly convex, and supports the optic nerves (where 



