74 



SKULL OF A 43-MM. HUMAN FETUS. 



directly continuous with Meckel's cartilage, show- 

 ing no evidence of the future separation. The 

 neck is relatively longer than in the adult con- 

 dition, and the manubrium is shorter. The 

 lateral process (fig. 42) is a distinct tubercle; here 

 the neck and manubrium join to form a gentle 

 curvature, with concavity upward and inward. 

 The chorda tympani lies just medial to this 

 between the processes of the malleus and incus. 

 The manubrium, from the processus lateralis to the 

 tip, is just medial to the stratum cutaneum of the 

 tympanic membrane. Medially it is inserted 

 into a distinct bay upon the lateral aspect of the 

 developing tympanic cavity (figs. 16 and 42), the 

 representative of the stratum mucosum of the 

 future tympanic membrane. The head shows a 

 ridge, edged with young cartilage, directed up- 

 ward and backward, which represents its spur or 

 cog-tooth. This is loosely fitted into the notch 

 upon the body of the incus. A small tubercle is 

 directed forward from the anterior aspect of the 

 head. 



The anterior process, or processus gracilis of 

 Folianus, is a slender spicule of very young bone; 

 indeed, most of the substance is composed of 

 osteoblasts with but little ground substance. It 

 arises in the perichondrium of Meckel's cartilage, 

 some distance below the head of the malleus and a 

 little below the chorda tympani nerve (figs. 31 

 and 34). It is attached to this perichondrium on 

 the caudo-medial aspect of the malleus, and the 

 spicule projects from this upward and a little 

 backward and outward, slightly approaching the 

 chorda, to end freely a little in front of the neck of 

 the malleus. A connection, however, is made 

 through connective tissue and the malleus shows 

 at this point a small amount of young cartilage 

 which indicates the future fusion of the process 

 to the neck. This bone, homologous with the 

 goniale of lower forms (Gaupp), was somewhat 

 farther developed in 7a. 



AUDITORY TUBE AND TYMPANIC CAVITY. 



The auditory tube comes off from the pharynx 

 just behind the level of the developing medial 



pterygoid plate and follows a course outward, 

 upward, and slightly backward. It is much flat- 

 tened from above downward and outward and 

 there is a very gentle curvature with concavity 

 downward and outward. At a point about half 

 way between the pharyngeal opening and the 

 caudalmost extremity of the tympanic cavity the 

 expansion for the latter begins to appear, and the 

 outer end of this epithelial evagination is very 

 broad and flat. When the entire structure is 

 looked at in frank view the medial border shows a 

 much stronger inward concavity than the lateral. 

 The tympanic cavity presents practically no 

 lumen, the walls being approximated. It lies 

 quite close to the promontory of the cochlea. The 

 medial aspect presents a shallow concavity and 

 the lateral aspect a corresponding convexity, 

 which, however, is even less marked. The upper 

 area is specially modeled, presenting a depression 

 (figs. 16 and 42) — representing the stratum 

 mucosum of the future membrana tympani — for 

 the manubrium of the malleus. From the superior 

 border of this depression there are tongue-like 

 prolongations which partially embrace the manu- 

 brium, as shown in figure 42. A little medial to 

 this upper edge is found the end of the crus 

 longum of the incus (fig. 16). There is a small 

 convexity upon the medial aspect corresponding 

 to the depression for the malleus (fig. 44). 



TYPE OF CARTILAGE. 



The type of cartilage of the otic region is almost 

 all mature. In the angular mass it is pale- 

 staining with sparse nuclei. The upper portion of 

 the cochlea shows a younger type of cartilage than 

 the remainder of the capsule. Edges of young 

 cartilage are found bordering the endolymphatic 

 and vestibular foramina, the spiral septum and the 

 small ridge upon the opposite wall, the outer edge 

 of the suprafacial commissure, and the joint sur- 

 faces of malleus and incus; and, upon the malleus, 

 the lateral process, the tip of the manubrium, and 

 the site of future union with the goniale. There 

 are no ossification centers. 



ORBITO-TEMPORAL REGION. 



The orbito-temporal or sphenoidal region con- 

 tains a central unpaired mass, representing the 

 body of the sphenoid, and three lateral paired 

 masses representing the two wings and the medial 

 pterygoid plates. 



The basisphenoid has been described with the 

 basal plate. The anterior end of its connection 

 with the cochlea juts out toward the side (fig. 10) 



and here forms part of the posterior boundary of 

 the carotid foramen. This projection represents 

 the posterior petrosal process of the mature bone. 

 The dorsum sellse, less developed than that of la, 

 is directly continuous with the basisphenoid and 

 is slightly concave anteriorly. It terminates in two 

 lateral, somewhat divergent and blunt tips, the 

 developing posterior clinoid processes. The upper 



