80 



SKULL OF A 43-MM. HUMAN FETUS. 



plate in front of this border is perforated by 

 several small holes. The sphenoethmoidal car- 

 tilage shares with the orbitosphenoid in the forma- 

 tion of the cartilaginous roof of the orbit and the 

 floor of the anterior cranial fossa. It is almost 

 I ilano, showing but a suggestion of a downward 

 concavity. 



The orbitonasal fissure (figs. 1, 5, 6) lies be- 

 tween the inner portions of the orbitosphenoid 

 and the spheno-ethmoidal cartilage. The cranial 

 border, irregular and broken by projections of 

 young cartilage from the spheno-ethmoidal car- 

 tilage, lies at a lower level than the caudal, which 

 it meets at a sharp angle, marking the lateral 

 limit of the fissure. The caudal border, rather 

 blunter, shows a gentle forward bend near the 

 point where it passes over upon the slender an- 

 terior root of the orbital wing. The medial border 

 may be followed forward along the laterally pro- 

 jecting edge of the sphenoidal limbus; from the 



cranial extremity of this it crosses over the surface 

 of the tectum nasi to join the cranial boundary. 

 The medial portion of the fissure will doubtless be- 

 come somewhat cut off by reason of the enlarge- 

 ment of the connection of the lesser wing with 

 the main stem. Laterally the fissure overlies the 

 orbital cavity, and medially its plane is above an 

 inward extension of this cavity overlying the 

 tectum nasi. 



TYPE OF CARTILAGE. 



The material of the orbitotemporal region is for 

 the most part mature cartilage. In the alar pro- 

 cess and greater wing, changes in the cartilage 

 have been noted which indicate the position of the 

 future centers of ossification here. There is rather 

 more precartilage and young cartilage than in the 

 posterior regions of the chondrocranium. The de- 

 tails have already been mentioned. 



ETHMOIDAL REGION. 



The ethmoidal region contains the mesethmoid 

 and paraseptal cartilages, the ectethmoids and 

 related cartilages. It is noticeably less developed 

 than that of 7a. 



MESETHMOID. 



The shape of the mesethmoid can be best ascer- 

 tained from figure 10. Three slender connections 

 with the ectethmoid are noted upon its upper 

 margin, while anteriorly there is a more elongated 

 union. The slightly thickened crista galli is 

 conspicuous above, and the upper border of the 

 septum for some distance behind this separates 

 the fenestra? crlbrosae (fig. 1). There is a small 

 union on either side with the paraseptal cartilage. 

 This was present on the right side only in 7a. 

 The mesethmoid is thinner than that of 7a and 

 does not possess such a thick lower border. There 

 is no indication of a superior paraseptal cartilage, 

 as in 7a. 



The ventrolateral processes are rudimentary, 

 being low ridges of very young cartilage extending 

 out slightly from the lower thickened border of the 

 septum (figs. 12, 13) just in front of the paraseptal 

 cartilages. For some distance behind these pro- 

 cesses the septal margin between the paraseptal 

 cartilages is of a very young type of cartilage, 

 covered with precartilage. 



Mucous membrane of septum. — Models have 

 been made of the mucous membrane covering the 

 medial (fig. 37) and lateral wall (fig. 38) of the 

 right nasal cavity. The mucous membrane of the 



septum, shown in figure 37 (which should be 

 compared with figure 10 to get the relation of the 

 membrane to the septum) shows a surface almost 

 plane. There is an exceedingly low, indistinct, 

 and wide elevation near its middle, which runs 

 almost parallel with the upper border of the sep- 

 tum. Very low hollows border this ridge. 



The vomeronasal or Jacobson's organ appears 

 upon either side of the nasal septum. In figure 37 

 the mucous membrane of the right side has been 

 cut away to expose the organ. It consists of a dor- 

 sal enlarged portion, of somewhat fusiform shape, 

 which terminates dorsocaudally in a fine point. 

 From the lower end a fine tube leads downward 

 and outward to empty into the lower portion of 

 the nasal cavity. The main mass of the organ is a 

 congregation of more or less uniform cells which 

 suggests a coiled tube, but the lumen is very 

 indistinct and the walls are made up of several 

 layers of cells. The septum does not show a dis- 

 tinct concavity for the organ, as in 7a. 



The paraseptal or Jacobson's cartilages (figs. 12 

 and 13) show a much younger type of material 

 and are more rudimentary in form than those of 

 7a, but the two main masses, medial and lateral, 

 may be recognized. 



The lateral mass is relatively small. It is 

 roughly of triangular shape, the apex being 

 directed forward, and being separated from the 

 fundament of the ventro-lateral process by a 

 narrow- cleft. This end of the plate is of pre- 

 cartilage. The base, of young cartilage, is con_ 



