SKULL OF A HUMAN FETUS OF 40 MM. 415 



Reichert's cartilages (figs. 2 and 4) are the paired cartilaginous 

 rods, lying below the posterior half of Meckel's cartilage, which 

 forai the posterior part of the hyoid arch. Each is roughly 

 the shape of a walking cane with a curved handle and a some- 

 what bent shaft. The handle-like portion is found between the 

 lower end of the crista parotica and the lateral extremity of the 

 jugular foramen, the fenestra perilymphatica being above it, and 

 the paracondyloid process below. It lies quite free in the mesen- 

 chyme, separated by that tissue from the otic capsule, a con- 

 dition agreeing with that described by Jacoby for an earlier stage, 

 in which the cartilages were in contact with the otic capsule, but 

 not fused with it, as they are shown to be in the Hertwig model 

 of a later stage. Each cartilage is of almost uniform diameter 

 throughout, and its direction is from behind forward, inward 

 and slightly downward, the shaft presenting a slight outward 

 and downward bowing, where it sweeps around the promontory of 

 the cochlea, and a gradual inturning toward the distal extremity. 

 As it passes forward the shaft gradually separates from the 

 promontory, to which it is closely approximated, without being 

 actually in contact, and at the same time draws closer to Meckel's 

 cartilage. The terminal anterior tip lies just medial to the angle 

 of the mandible (fig. 2), and above the greater cornu of the 

 hyoid cartilage, which it overlaps for a short distance, without 

 actually becoming contiguous, and it shows a rather younger 

 type of cartilage than the rest of the shaft. The latter differs 

 from that of the chondrocranium in being more reddish in stain. 



MEMBRANE BONES 



All of the purely membrane bones of the skull are represented 

 in my embryo, though they are as yet but imperfectly developed. 

 The interparietal appears, as has been noted, just lateral to the 

 dorsal occipital prominence as a faintly staining spicule of osseous 

 matter, but owing to the lack of the dorsal sections the extent 

 of the bone could not be ascertained, and hence it was not shown 

 in the model. Though this bone does not appear in the model 

 of Hertwig it must have been present, as this embryo was con- 



