1 10 ELEMENTAR Y ANA TOM Y. [LESS. 



it may also be represented by the sphenotic, which in bony 

 Fishes unites with the pterotic to furnish the point of suspen- 

 sion for the lower jaw. 



The so-called external pterygoid process of man is really 

 but an outgrowth of the alisphenoid, and must be considered 

 with it. This part is absent in all animals below Birds, and 

 in Birds where it exists, e.g. in the Finches (Fringilla), it is 

 represented by but a single or double ridge. 



In Mammals generally, however (except the Echidna), it is 

 present, and more or less as in man, though mostly it is 

 larger and less deep vertically. 



The external carotid artery may pierce the root of this part 

 (as in the Dog), forming thus a special bony channel called 

 the alisphenoid canal. The third branch of the fifth nerve 

 may pass more anteriorly with regard to this bone than in 

 man, as is the case in the Sheep. On the other hand, it gene- 

 rally passes out altogether behind it. A vidian canal is often 

 much more conspicuous than in him, e.g. in the lower Apes. 



A distinct foramen rotundum is often present and often 

 absent. In the latter case, the second branch of the fifth 

 nerve passes out through the sphenoidal fissure, as e.g. in the 

 Hare, Squirrel, and Stag. 



Each of the lesser wings of the sphenoid is termed in 

 zootomy an orbito-sphenoid, and in some forms, e.g. in Rumi- 

 nants, the proportion they bear to the alisphenoid is the 

 reverse of that which obtains in man, so that the application 

 to them generally of the name they bear in anthropotomy, 

 "lesser-wings," would be manifestly out of place. These 

 bones are constantly present in man's class, but, unlike the 

 alisphenoid, are often absent in the class of Birds, though 

 present in many kinds (e.g. Accipiter and Tinamus). They 

 are mere rudiments in most Reptiles often altogether absent 

 though they maybe developed in Lizards. In Batrachians 

 they may be well developed, or coalesce (as in Frogs and 

 Toads) with the ethmoid in a way to be described in treating 

 of that bone. In Fishes they are generally absent, but may be 

 well developed, as in the Carp, where however they form one 

 bone with the pre-sphenoid. 



Occasionally, as in the Hare, they may be so disposed as to 

 constitute a median, interorbital septum, the two optic fora- 

 mina having become merged one in the other. 



The optic foramen may be excessively minute, as in some 

 Insectivora, and there may be a foramen passing from orbit 

 to orbit beneath it, as in Macroscelides. 



