384 ROBERT J. TERRY 



A word may be said regarding the membranous structure here 

 called septum transversum. The development, in its basal part, 

 of a marked thickening which extends from the crista transversa 

 to the parietal plate, together with the presence in it of a carti- 

 laginous bar over the semilunar ganglion are suggestive of struc- 

 tures in the reptilia, such as Shino ('14) has described in the 

 crocodile and compared with the pila prootica of Lacerta. A 

 cartilage over the semilunar ganglion in Lepus recorded by Voit 

 was interpreted as a vestige of the primary cranial wall; in the 

 cat, a cartilaginous mass, having the same position and relations, 

 was found within the septum transversum. 



Ala orhitalis. The occurrence generally, in a wide range of 

 types, of the independent origin of the ala orbitahs has been em- 

 phasized by Noordenbos. This phenomenon,' as shown above, is 

 also characteristic of the cranial development of the cat. The idea 

 of the association of the ala orbitalis, primarily with the optic 

 nerve and eye-ball, seems to be well founded and receives further 

 support from the early form and relations of this cartilage in the 

 cat. The relations of the origins of the ocular muscles may be 

 interpreted as further indicating a close connection between the 

 orbital wing and the organ of sight. The definitive origins of 

 these muscles are in the main related to the optic foramen, about 

 as they are in the chondrocranium, but some shifting has evi- 

 dently taken place as comparison of the two states shows (Wilder 

 and Gage '86; Corning '02). Four definite separate spots in the 

 chondrocranimn are occupied by, and one of them apparently 

 specially adapted to, the attachment of the muscles of the orbit. 

 How these attachments compare with those in the mammaUan 

 types represented in the literature of the chondrocranium I can- 

 not say, since this question does not seem to have received atten- 

 tion. Does the superior obhque constantly spring from the 

 preoptic root; does the orbital process of the metoptic root 

 function generally as a point of attachment of a definite group of 

 eye-muscles; is the side of the basis cranii in the orbital fissure 

 a special locus of origin of another group, and is the origin of 

 the inferior oblique constantly the planum antorbitale? Regard- 

 ing the metoptic root, it has been noted that, in contrast to the 



