328 ROBERT J. TERRY 



the beginning of the crista transversa. This is the stage of 

 precartilaginous structure of the alar and commissural elements. 

 The latter is continuous with the side of the sella turcica and sep- 

 arated from the alar element by an oblique layer of mesenchyma. 

 The boundaries of the carotid foramen are well defined, the me- 

 dial boundary being formed by the posterior part of the side of 

 the sella turcica ; the caudal limit by the prochondral union of the 

 basal plate and cochlear capsule, the commissura basicochlearis; 

 the anterior and lateral by the prochondral commissural element. 

 The alar element has a homogeneous structure of young cartilage 

 and is now recognizable as the ala temporalis; both the mandibu- 

 lar and maxillary nerves pass through notches in its margins. 



In van Wijhe preparations of 15 mm. (fig. 7) a continuous 

 stretch of cartilage occurs in the floor of the cranium in the otic, 

 hypophyseal, trabecular and nasal septal regions. The tubercu- 

 lum sellae is apparently developed from the caudal and dorsal 

 edge of the trabecular plate. The junction of the basal plate 

 and floor, in the hypophyseal region, is marked by a broad ex- 

 pansion of lightly stained tissue (young cartilage). In a median 

 section (fig. 18) the cartilage in the septum transversum behind 

 the hypophysis, present in the preceding stage, appears as a 

 small nodule. The ala temporalis is represented by a slender 

 sickle-shaped cartilage standing ventrad of the anterior pole of 

 the semilunar ganglion. It is laterally removed from the sella 

 turcica and from the commissural element (the interval is ex- 

 aggerated in figure 7). In the epipteric region the membrana 

 limitans is clearly defined throughout. The origin of the trans- 

 verse septum is' marked by a band-like thickening, extending from 

 the crista transversa laterad over the semilunar ganglion and roots 

 of the trigeminus, and terminating on the supraf acial commis- 

 sure and parietal plate. 



The pterygoid presents no important change from the preced- 

 ing stage. Chondrification of the ala orbitahs has begun over 

 the eye-ball in the form of a triangular plate, separate from all 

 neighboring cartilages (fig. 7). Posterior to the orbital ala is 

 the independently chondrifying commissura orbito-parietalis ; far 

 removed anteriorly are the cartilages of the nasal, capsule. One 



