PRIMORDIAL CRANIUM OF THE CAT 379 



The differences between the independent ala temporahs of the 

 cat and the continuous ala of the mole are apparent rather than 

 real. A very simple explanation removes these apparent differ- 

 ences. 1) The alar element of the cat is wanting in a medial 

 part, comparable with the origin of the anterior process from 

 the pole-plate in the mole. Excepting in the undifferentiated 

 mesenchymal continuity of the alar element and anterior limb 

 of the commis.sural element, there is no indication of a connection 

 between it or its derivative, the ala temporalis, and the side of 

 the sella turcica. 2) The processus alaris is compound in the 

 mole, being derived from the root of the anterior process plus 

 the anterior limb of the middle process; it is simple in the cat, 

 being composed of the anterior limb of the commissural element 

 only. The processus alaris of the cat is therefore comparable 

 with only the caudal part of the ala temporalis of the mole, i.e., 

 with that part derived from the anterior limb of the middle 

 process. 3) The alar element of the cat and its derivative fails 

 to unite with the commissural element and its derivatives, and 

 there remains throughout the cartilaginous stage of the ala tem- 

 poralis, a synchondrosis representing the limiting margins of the 

 two elements. In the mole, partial fusion takes place between 

 the comparable elements, but a cleft-like vestige remains locat- 

 ing the original separating space. Perhaps the conditions in 

 the hedge-hog and bear described by Wincza may be similarly 

 explained. 



The conclusions reached therefore are : 1) the reduction or the 

 absence of a medial part of the alar element of the cat, compara- 

 ble with the origin of the anterior process from the sella turcica 

 of mole; 2) the presence of a simple processus alaris in the cat, 

 of a compound one in the mole ; 3) the persistence of the original 

 boundary between the lateral and commissural elements in the 

 cat and the obliteration of the limits between the comparable 

 anterior and middle processes in the mole. It follows that the 

 ala temporahs of mole and cat are in the main comparable. It is 

 probable that other examples of the types of continuous and inde- 

 pendent temporal wings may be similarly explained. 



