76 



SKULL OF A 43-MM. HUMAN FETUS. 



found thorn present in the sphenoid of a young 

 adult in t ho osteological collection (No. 101) of 

 the Johns Hopkins .Medical School. The skulls 

 in which they were absent were apparently from 

 old individuals. 



INTERORBITAL SEPTUM. 



The part of the central stem forming the 

 narrow medial delimitation of the orbital cavities 

 is known as the interorbital septum. Its anterior 

 end lies above the level of the posterior extremity 

 of the ectethmoid. It is much reduced in area in 

 the human subject as compared with lower forms. 

 It extends forward slightly beyond the limbus 

 sphenoidalis, coming to an end at the point where 

 the attachments of the ectethmoid reach to the 

 upper margin of the septum. 



Anterior to the sulcus chiasmatis the upper 

 border of the interorbital septum passes forward 

 and slightly upward to reach a distinct eminence, 

 the limbus sphenoidalis. Its upper narrow ex- 

 tremity is prolonged laterally into thin ridges, to 

 which, at bilaterally opposite points, are attached 

 the small preoptic roots of young cartilage. It is 

 to the posterior aspect of these roots that the 

 anterior extremities of the prechiasmatic com- 

 missures are attached. 



In front of the limbus sphenoidalis is a much 

 smaller notch, followed by a low but distinct 

 eminence, capped by young cartilage. Some- 

 where in this region is the position of the future 

 sphenoidal spine, although there is nothing here 

 in the condition of the cartilage indicative of the 

 future separation of the sphenoidal and ethmoidal 

 elements of the septum. This ridge presents, 

 on either side, very slender connections with the 

 roof of the ectethmoid, and directly behind this 

 are two other junctions with the same structure. 

 These attachments, of which there are thus three 

 on either side, are separated by minute foramina 

 and lie in almost a straight line (fig. 10). The 

 eaudalmost junction is below the limbus. They 

 spring from a ridge of cartilage which projects 

 laterally from the septum. The anterior end of 

 this is level with the upper edge of the septum, 

 but the posterior end is some distance below the 

 limbus, as figure 10 shows. 



In front of the eminence just described the 

 upper border passes forward upon the nasal 

 septum, descending into a distinct notch and 

 rising upon the very prominent crista galli, to fall 

 away finally upon the anterior border of the 

 mesethmoid. 



The lower border of the body of the sphenoid, 

 or more accurately here, the presphenoid, after 



leaving the distinct notch beneath the floor of the 

 hypophyseal fossa, follows an almost direct 

 course downward and forward, as figure 10 shows. 

 Somewhere in the vicinity of the dorsal extremity 

 of the vomer we have to place the ventral limit 

 of the presphenoid, though, as with the upper 

 margin of the plate, there is no trace of any de- 

 limitation. 



PROCESSUS ALARIS. 



The temporal wing proper is supported by the 

 processus alaris (figs. 1, 2, 15), a short, rather 

 plate-like rod of cartilage, flattened from above 

 downward, which projects laterally at right angles 

 to the body of the sphenoid, with but a very slight 

 inclination downward. Its medial extremity, of 

 which the cut edge appears in figure 15, is thin, and 

 is attached to the lower surface of the body of 

 the sphenoid, as shown in figure 10. The lower 

 surface shows a slight concavity from before 

 backward, and the upper surface a corresponding 

 convexity. There is upon the upper surface, too, 

 a slight side-to-side concavity, and in this the 

 internal carotid artery lies (fig. 15). It is the 

 representative of the future sulcus caroticus. 

 The sulcus is bounded laterally by a raised, knob- 

 like eminence, which marks the latero-dorso- 

 caudal extremity of the alar process, and from 

 this is directed, backward and slightly upward 

 and outward, the alicochlear commissure (fig. 6), 

 a well-marked spur of cartilage. This, it will be 

 remembered, is confluent bj r its slender caudal tip 

 with the cochlea just below the cranial pole. 

 From its relation to the internal carotid artery 

 and to the sphenoidal fundament, it is undoubt- 

 edly the primitive lingula which, in the mature 

 skull, is formed of bone and projects backward 

 into the foramen lacerum, often being quite 

 elongated. Although the slender junction of this 

 commissure with the cochlea is of young cartilage, 

 the knob-like eminence from which it springs 

 shows slight changes in the cartilage premonitory 

 of ossification. This region represents the sphe- 

 notic center. Fawcett (1910) describes this 

 independent center in a 110-mm. human embryo 

 and remarks: 



"Its large size is somewhat surprising, if it 

 form only that part commonly in our text-books 

 called lingula. From its posterior end a pointed 

 cartilaginous process is seen to pass backwards 

 towards the auditory capsule." 



The alar process, thus, is for the most part in- 

 cluded in the body of the mature bone rather 

 than in the greater wing. Its outer extremity, 

 with the continuation into the alicochlear com- 



