CARTILAGINOUS SKULL OF A 21 MM. HUMAN EMBKYO. 309 



since, in the passage of the nerve from the geniculatc ganglion to the spheno- 

 palatine ganglion, part of its course is just beneath the alar process medial to the 

 medial end of the temporal wing proper. It is here that the junction of the body 

 with the temporal wing and the pterygoid process occurs and where later develops 

 the pterygoid canal (fig. 13). Only the lateral part of the ala temporalis of the 

 embryo, then, corresponds to that part of the temporal wing of the adult which 

 ossifies in cartilage. In the adult the carotid sulcus and the lingula are at a higher 

 level than the temporal wing, a condition which exists in the embryo if we consider 

 the alar process as forming a part of the body of the sphenoid. 



Since most of the temporal wing and both plates of the pterygoid process are 

 ossified in membrane, the cartilaginous wing, even when fully developed, repre- 

 sents but a small part of the temporal or greater wing and pterygoid process of the 

 adult. The maxillary nerve lies in front and the mandibular nerve behind this 

 cartilage. In later stages the cartilage grows around the maxillary nerve and 

 separates it from the supraorbital fissure, thus forming the foramen rotundum 

 (figs. 3 and 10). Cartilage does not grow around the mandibular nerve, and the 

 foramen ovale is said to be formed by membrane bone. At this stage, therefore, 

 the large cleft between the temporal wing and the orbital wing represents more 

 than the supraorbital fissure. 



The alar process and the temporal wing proper each has its own center of 

 chondrification, as pointed out by Bardeen and Fawcett. The alar process chondri- 

 fication unites with the basisphenoid before the temporal center unites with the 

 alar process. 



The cartilaginous orbital wing, like the temporal wing, is very incompletely 

 developed, as will be seen by comparing it with the older stages of Levi, Macklin, 

 and Hertwig. It consists of two parts, a proximal or basal part, and a lateral, 

 sickle-shaped part, which springs upward, outward, and forward around the optic 

 nerve and has much the same general position as that part of the orbital wing 

 immediately about the optic nerve of the adult. The basal part of the orbital 

 wing is connected to the basisphenoid by young cartilage and to the lateral part 

 by cartilage not quite so far advanced as that in either the basal part or the lateral 

 part. It seems probable that both parts of the orbital wing may arise from inde- 

 pendent centers of chondrification. From the general position of this basal part 

 and its relation to the optic nerve and to the general mesenchyme of this region, 

 and from the fact that it gives origin to all of the muscles of the orbit except the 

 superior oblique, I think it must ultimately become incorporated into the body of 

 the sphenoid. The sickle-shaped lateral part of the orbital wing is intimately 

 related to a larger precartilaginous part indicated by the green-colored structure 

 in figure 3. This precartilaginous part shades off into the frontal blastema and 

 there is in reality no sharp line between the two. The cartilaginous and pre- 

 cartilaginous parts together have somewhat the same form as the orbital wing of 

 the 40 mm. embryo described by Macklin. 



