380 ROBERT J. TERRY 



Whether the lamina ascendens of the cat should be regarded 

 as an independent element in origin, or continuous with the basis 

 cranii, is a question which could be answered either way from the 

 evidence here presented, and would be purely a choice of inter- 

 pretations. The whole ala temporalis is shadowed in mesen- 

 chyma, continuous with the basis cranii; in this adumbration 

 condensations appear which are distinct from one another or 

 confluent at the edges, as you choose to describe the conditions. 

 Comparison of the lateral element of the cat with the anterior 

 process of the mole inclines me to regard this element and its 

 derivative, the ala temporalis, as not an independent element 

 genetically. There appear to be two parts under consideration 

 in comparisons of the ala temporalis of different mammals, (1) 

 a part which is related chiefly to the carotid artery, represented 

 by the middle process of the mole and the commissural process 

 of the cat; (2) a part which is related to the semilunar ganglion 

 and the three divisions of the fifth nerve. These two parts 

 are typically both connected with the cranial base, the one arch- 

 like, the other process-like. Both are typically originally sepa- 

 rate from one another, the process standing in front and at the 

 side of the arch. In some forms the process unites with the arch 

 completel}^ (mole), in others partially (hedge-hog), instill others 

 not at all (polar-bear, cat). Finally, this conception of the com- 

 parison of the anterior process of mole and the ala temporalis of 

 cat, supports the homology of the ala temporalis of placental 

 maminials with the ala temporahs of Echidna. 



Pterygoid. The pterygoid cartilage is developed relatively late, 

 not until after bone has begun to be formed in its dorsal part. It 

 is represented by a rather ill-defined mesenchymal condensation, 

 even at the time when the ala temporalis is w^ell chondrified. 

 Only its caudal part is cylindrical and thus bears some resem- 

 blance to the cartilage of the medial lamella of the pterygoid proc- 

 ess in Talpa. It is unlike this process in not reaching forward to 

 the ethmoidal region. How^ever, as pointed out, it develops in 

 the same morphological plane as the palate bone, lies next the 

 ductus nasopharyngeus, in front of the first pharyngeal pouch 

 and is crossed dorsad by the Vidian nerve. 



