308 CARTILAGINOUS SKULL OF A 21 MM. HUMAN EMBRYO. 



cerebelli. The boundaries of the middle cranial fossa are more clear in figure 3, 

 where the lateral blastemal walls are shown. The temporal wing extends into 

 this lateral blastema and thus completes the medial portion of the floor of the 

 middle fossa. Between the temporal wing and the otic capsule is the large middle 

 lacerated foramen, through which pass the internal carotid artery and the mandib- 

 ular nerve. The facial nerve, with the geniculate ganglion and the greater super- 

 ficial petrosal nerve, also passes through the foramen. The large otic ganglion lies 

 across the foramen (figs. 12 and 13). The precartilaginous tissue attached to the 

 anterior aspect of the temporal wing completes the foramen ovale and separates it 

 from the supraorbital fissure. Between the temporal wing and the orbital wing, 

 with its precartilage, is the large supraorbital fissure, and through it the oculomotor, 

 trochlear, abducens, and ophthalmic nerves pass into the orbital cavity (fig. 15). 



The embryonic tentorium cerebelli consists of two lateral prismatic masses of 

 mesenchyme connected across the midline by a band of condensed mesenchyme 

 that extends upward from the whole breadth of the dorsum sellae. The bases 

 of the prisms are against the lateral walls of the membranous skull and the apical 

 edges at the membranous band that extends upward from the dorsum sellse. The 

 lower end of each prism fills one of the lateral depressed areas of the potential 

 middle cranial fossa, between the otic capsule in back, the orbital wing in front, 

 and the lateral wall of the membranous skull. The posterior wall of each pris- 

 matic mass of the tentorium is composed of a thin layer of condensed mesenchyme, 

 and its lower edge is attached along the anterior edge of the otic capsule and 

 extends upward. The anterior wall of each prismatic mass, likewise composed of 

 a thin layer of condensed mesenchyme, is attached to the posterior border of the 

 orbital wing and its precartilage and extends upward. These two membranes 

 come together along the medial apical edge where they are continued into the 

 medial connecting band. Laterally, the two membranes fuse with the lateral 

 membranous wall of the skull. The interior of each prism is filled with loose 

 mesenchyme in which are imbedded the semilunar ganglion, large blood-vessels, 

 and nerves. The trochlear and oculomotor nerves pass from above downward 

 through the entire length of the prism. The tentorium obliterates entirely the 

 potential middle cranial fossa. Later, when this fossa develops, the anterior wall 

 of the tentorium must be pushed down and back into the floor and against the 

 posterior wall of the fossa. 



Each ala temporalis consists of two distinct parts, a medial alar process joined 

 to the basisphenoid by young cartilage, and a lateral part which is, more strictly 

 speaking, the cartilaginous temporal wing. It is attached to the under surface of 

 the alar process by condensed mesenchyme and lies at a lower level (figs. 1, 2, 3, 

 5, 6, 10, 11, and 14). Each alar process is usually regarded as forming the lingula, 

 but since the internal carotid artery, which enters the cranial cavity between it 

 and the apical end of the otic capsule, passes over its cranial surface, it seems 

 probable that it gives rise as well to that part of the basisphenoid which forms the 

 carotid sulcus. The relation of the greater superficial petrosal nerve to the alar 

 process also indicates that the latter is incorporated into the body of the sphenoid 



