$20 ROBERT J. TERRY 



joining beneath the lamina the great^ deep petrosal nerve to form 

 the N. pterygoideus. Incisura lacera is the name proposed for 

 the deepest part of the fissura alicochlearis, a part distinguished 

 by certain important relations. It reaches medially toward the 

 carotid foramen, from which it is separated by the commissura 

 alicochlearis, and here adjoins the posterior end of the mesen- 

 chymal zone dividing the commissure from the lamina ascendens. 

 A prominent spine of the caudal margin of the ascending plate 

 forms its antero-lateral boundary and stands between it and the 

 incisura ovalis. On the anterior margin of the ala temporalis, 

 adjacent to the processus alaris, is the broad processus pterygoid- 

 eus (fig. 1), in connection with which is later formed the insignifi- 

 cant bony lamina lateralis processus pterygoidei of the adult. 

 The pterygoid process projects forwa'd and toward the mid- 

 plane, lying medial of the foramen rotundum. Its medial end 

 is separated from the adjacent pterygoid cartilage by a layer of 

 mesenchyma. At this spot the Vidian nerve begins to turn from 

 beneath the lamina ascendens to gain, eventually, a position dor- 

 sad of the pterygoid cartilage and within the spheno-orbital 

 fissure. 



The base of the ala temporalis is directed obliquely from be- 

 hind, forward and medialward and for the most part corresponds 

 to the synchondrosis between the ascending plate, alar process 

 and alicochlear commissure. Two other regions, however, must 

 be included in the base: posteriorly, the medial free margin of 

 the spine separating the incisura lacera from the incisura ovalis, 

 and anteriorly, the medial free margin of the processus pterygoid- 

 eus. The relations into which the base of the ala enters with 

 the rest of the chondrocranium are, therefore, the medial corner 

 of the spheno-orbital fissure, processus alaris, commissura ali 

 cochlearis and incisura lacera. 



Ala orhitaUs (figs. 1, 2, 3, 4). This great sickle-shaped carti- 

 lage forms, on each side, the larger part of the medial wall of the 

 orbit and the lateral wall of the fore part of the cranial cavity. 

 Its lateral and medial surfaces are respectively concave and con- 

 vex, apparently in adaptation to the eye-ball and its adnexa. 

 The anterior extremity is joined to the nasal capsule by the com- 



