382 ROBERT J. TERRY 



affecting the question of the nature of the region about the ca- 

 rotid artery. In Echidna the carotid enters directly the primary 

 cranial cavity, but the position of the foramen through which it 

 passes lies within the lateral confines (trabecula basis cranii) of 

 the hypophyseal fossa and therefore may be compared with the 

 entrance into the cranium of this vessel in Lacerta. In placental 

 mammals the carotid foramen lies laterad of the sella turcica, a 

 position which has been explained by two assumptions: (a) lat- 

 eral migration of the vessel, (b) non-equivalency of the mammal- 

 ian and reptihan carotid. In accordance with the theory of lat- 

 eral migration, the carotid foramen is supposed to have moved 

 outward across that part of the cranial floor equivalent to the tra- 

 becula; or both the trabecula and artery have moved lateral 

 while still retaining their primitive relations to each other. The 

 trabecula cranii of Lacerta is represented in mammals, accord- 

 ing to Gaupp ('02), by the ahcochlear commissure. The unity 

 of this commissure, including both the processus alaris and com- 

 missura aUcochlearis, its distinction from the ala temporalis, and 

 its relation to the base of the cranium were recognized by Gaupp. 

 In one place ('06), he says: "The processus alaris of man appears 

 as a process only through the decadence of the cartilaginous 

 bridge which closes laterally the carotid foramen. It belongs to 

 the median cartilaginous mass in the base of the orbito-temporal 

 region," Voit, who has advocated the view of non-equivalency 

 of the internal carotid in mammal and reptile, locates the carotid 

 foramen in Lepus laterad of the trabecular region. He concludes 

 that the commissura alicochlearis plus the processus alaris alae 

 temporahs should not be compared with some part of the tra- 

 becula, but rather the processus alaris should be referred to the 

 processus basipterigoideus of Lacerta and ala temporalis of 

 Echidna. The commissura alicochlearis is regarded by Voit as a 

 new structure, in mammals, in the floor of the epipteric cavity, a 

 continuation of the floor of the cavum supracochleare. Fuchs 

 ('10) also, compares the medial part (root) of the ala temporalis 

 with the processus basipterigoideus of reptiles. In accordance 

 with Voit's interpretation, the carotid artery first enters the epi- 

 pteric cave, then, after traversing the medial limiting membrane 



