82 



SKULL OF A 43-MM. HUMAN FETUS. 



terior prominence there is a distinct cleft. Pro- 

 jecting forward from it is a hardly distinguishable 

 osseous fragment — the beginning lacrimal bone. 

 Immediately lateral is the hook-like paranasal 

 process which shows a rather knobbed extremity, 

 lying somewhat below the level of the lacrimal 

 bone. The process projects downward and for- 

 ward and its pedicle is slightly constricted. It is 

 of a young type of cartilage. In la, it was dis- 

 connected from the wall. Medial to the process 

 is the lacrimal duct (fig. 39). 



Paranasal process. — The wall to which the 

 paranasal process is attached is the widest part of 

 the lower border of the antorbital plane. This 

 ridge continues anteriorly, with an inward, up- 

 ward, and forward curve, upon the posterior prom- 

 inence. It corresponds to the deepest part of 

 the middle meatus. 



It is convenient here to examine the inferior 

 concha, which forms the greatest part of the floor. 

 It is inclined a little downward and shows a 

 downward-looking, wide, shallow groove. This is 

 of thin young cartilage. It is represented in the 

 floor of the middle meatus by a low, rounded 

 anteroposterior ridge. The free border of young 

 cartilage is thickened and turned downward and is 

 somewhat irregular. The caudoventral angle 

 is rounded and the caudal border shows a back- 

 wardly projecting, short point, surmounted by a 

 low vertical ridge of precartilage. Between this 

 point and the ventrolateral angle of the plane 

 there is a notch, the representative of the ventral 

 palatine notch of la, which, however, is small when 

 compared with the older stage. In it is found the 

 anterior extremity of the palate bone (fig. 41). 

 The concha gradually projects more steeply 

 downward, as it is followed forward, and comes to 

 an end some distance below the posterior prom- 

 inence at the post-transverse incisure. 



The anterior or nasal portion of the wall is more 

 irregular than the posterior. Above appears the 

 small superior prominence, which is not rep- 

 resented upon the internal surface by a concavity. 

 A little below and behind it is the foramen epi- 

 phaniale. The middle prominence (called by 

 Yoit the supraconchal prominence or Sakterwulst) 

 in less conspicuous than in la. Overlying it is a 

 band of mesenchyme continuous with the frontal 

 process of the maxilla. A corresponding but 

 relatively less marked concavity appears upon the 

 inner surface. Although there is a slight depres- 

 sion here in the mucous membrane, which is con- 

 tinuous caudodorsally with the cleft for the mid- 

 dle meatus, yet it is not so prominent as the emi- 

 nence on the outer surface would lead us to 



expect. The inferior prominence, in front of the 

 paraseptal process, is quite evident. 



Cupular process. — The lower margin, at the 

 front of the anterior naris, presents several pro- 

 jections. Anteriorly is the curious, slender, hook- 

 like cupular process of precartilage (figs. 38, 39, 

 40, 41), which is an extension of what I termed 

 the cupular cartilage. It extends for 700 micra 

 anteroposteriorly. It at first curves sharply 

 inward, coming to underlie the septum and also to 

 lie quite close to its neighbor of the opposite side. 

 It terminates in a sharp tip turned outward and 

 backward. Only its stump was described in la. 

 It shows a distinct outward concavity which 

 embraces the epithelial plug of the anterior naris, 

 as shown in figure 40. Rehmke (1913), according 

 to Peter (1913), showed that this process later 

 becomes cartilaginous and forms the medial crus 

 of the greater alar cartilage, and that in doing 

 so it fuses with what seems to correspond to the 

 ventrolateral process. Rehmke's latest stage 

 was 275 mm. sitting height (30-32 weeks). 



Behind this process is a notch and the edge 

 here is of very young cartilage. We then come 

 upon the superior alar process, which projects 

 downward from the lower edge of the inferior 

 prominence. Behind this is the distinct para- 

 septal process, terminating in a point of precar- 

 tilage which projects backward and upward. 

 It forms the lower border of the post-transverse 

 incisure. This incisure is made a foramen by the 

 lower edge of the maxilla. Both the superior 

 alar process and the paraseptal process are found 

 in Rehmke's figures in Peter's Atlas. The former 

 is included in the lateral crus of the greater alar 

 cartilage, while the latter breaks up to form the 

 lesser alar cartilages, as shown in Peter's figure 

 56d, from the 275 mm. stage. 



The interior of the ectethmoid (figs. 41 and 43) 

 presents all the young conchae. There are three 

 slender connections above with the nasal septum 

 and anteriorly an elongated union with the septum 

 appears. These all fit to the cut edges shown 

 upon the septum in figure 10. Behind the pos- 

 terior connection is seen the down-turned edge of 

 young cartilage already mentioned. This was 

 more advanced in la, where the appearance sug- 

 gested a concha. Just below it, and above the 

 posterior end of the superior concha, is a space 

 which represents the spheno-cthmoidal recess. 

 The superior concha is short, broad centrally, and 

 low. It is of very young cartilage, with an envel- 

 opment of precartilage. The anterior extremity 

 is rather narrow and turned downward. Under- 

 lying this concha is the shallow superior meatus. 



