320 CARTILAGINOUS SKULL OF A 21 MM. HUMAN EMBRYO. 



to the lateral part by blastema. We have already given sufficient consideration to 

 the fate of the alar process and its probable incorporation into the body of the 

 sphenoid, and also the lateral part which corresponds more strictly to that part of 

 the temporal wing that ossifies in cartilage. This part of the cartilage is still incom- 

 pletely developed; as in later stages the cartilage extends around the maxillary nerve. 

 The orbital wing is even more immature than the temporal, as will be seen by 

 comparing it with the older stages of Macklin and Hertwig. In figure 3 is shown the 

 precartilaginous part, which is more extensive than the cartilaginous part. The 

 basal part of the orbital wing lies at the apex of the orbit and gives attachment to 

 all the muscles of the orbit except the superior oblique (figs. 10 and 15). 



THE TEMPORAL CARTILAGE. 



This cartilage includes the otic capsule and the mastoid cartilage, which are 

 intimately fused together. 



OTIC CAPSULES. 



The otic capsules form the cartilaginous basis for the petrous bones of the 

 adult. They are very prominent, being striking features of the chondrocranium, 

 and extend on each side in a caudo-dorso-lateral direction to the lateral surfaces 

 of the skull. Each capsule consists of two broadly united and continuous parts 

 (a medial cochlear part and a lateral canalicular part) inclosing the cochlear and 

 semicircular canals respectively. The two parts are more or less set off from 

 each other by a broad shallow groove, the capsular sulcus. 



The cochlear part is somewhat egg-shaped and fuses with the basioccipital. 

 The cranial surface is rounded and presents the large, rounded, internal acoustic 

 meatus. The ventral surface is also rounded and projects below the level of the 

 basioccipital, forming with it a distinct groove. The cochlear part consists of 

 somewhat younger cartilage than the canalicular part. Its relation to the cochlear 

 duct is shown in figure 16. 



The capsular sulcus extends entirely around the otic capsule. On its anterior 

 surface is a large foramen for the exit of the facial nerve. This foramen is separated 

 by a narrow bar of cartilage from the internal auditory meatus. The facial nerve 

 has but a very short course within the otic capsule ; the geniculate ganglion and the 

 nerve distal to it are outside of the capsule, but close against it (figs. 12 and 13). 

 The capsular sulcus is broad and shallow on the inferior surface and near its center 

 lies the fossa vestibularis or ovalis, in which is imbedded the base of the stapes. 

 Immediately about the fossa is an area of young cartilage; the floor of the fossa 

 is also covered with young cartilage. The posterior part of the sulcus, which 

 borders the jugular foramen, contains the opening for the aqueductus cochlearis. 

 At this stage only a small plexus of veins pass through it, but later it contains the 

 perilymphatic duct. 



The canalicular part of the otic capsule constitutes the lateral half and forms 

 part of the outer wall of the chondrocranium. It is more or less oval in form 

 and flattened in a medio-lateral direction. It consists for the most part of the 

 thickened cartilaginous covering for the semicircular ducts. The locations of 



