PRIMORDIAL CRANIUM OF THE CAT 321 



missura spheno-ethmoidalis ; the posterior extremity is connected 

 wdth the fore part of the basis cranii by two roots, named preoptic 

 and metoptic, relative to the optic nerve which they embrace. 

 The preoptic root is broad and straight whereas the metoptic 

 root is narrow and bent so as to present a prominent angle of its 

 caudal margin directed backward. The optic foramen, large and 

 irregulary oval, is bounded medially by the basis cranii, on its 

 other sides by the orbital wing and its two roots. Through the 

 optic foramen a short, blunt process, processus orbitahs, extends 

 into the orbit from the cephalic edge of the metoptic root. On 

 the right side this process Ues close to the basis cranii. From -the 

 roots of the orbital wing some of the ocular muscles take origin 

 (vide infra). The short concave, anterior margin of the wing is 

 free and separated from the nasal capsule by the fissura orbito- 

 ethmoidalis. This is filled by membrane and transmits the lat- 

 eral branch of the nasal nerve. The extensive, convex, posterior 

 margin, dorsally, passes into the commissura orbito-parietahs con- 

 necting the orbital wing with the parietal plate, and ventrally 

 is free in the anterior boundary of the fenestra spheno-parietalis. 



The spheno-orbital fissure (Wincza, '98) (figs. 1, 2, 3, 4, 23) 

 in the present stage stands in marked contrast to the circular, 

 completely walled opening of the adult cranium. It is a narrow, 

 deep gap running in a frontal plane between the ala orbitalis 

 above and the ala temporaUs and pterygoid cartilage below. It 

 is open laterally, but closed medially by that part of the basis 

 cranii lying between the metoptic root of the ala orbitahs and 

 the processus alaris. It gives passage to the oculomotor, pathetic, 

 ophthalmic and abducent nerves, together with a number of 

 veins which go to join the plexus about the semilunar ganghon 

 and carotid artery. 



The carotid foramen (figs. 1, 2) is completely w^alled, as de- 

 scribed by Decker and later by Wincza. It is circular, not large 

 as compared with that in Lepus, stands opposite the middle of 

 the sella turcica and traverses the floor of the skull straight ven- 

 tro-dorsad. In front is the processus alaris; behind, the coch- 

 lear capsule; laterally, the aUcochlear commissure. Upon its 

 medial side is the sella turcica. 



