398 CHARLES CLIFFORD MACKLIN 



the tegmen tjrmpani and its forward extension, and the com- 

 missura ahcochlearis, together with the osseous elements formed 

 by the parietal, and squamous portion of the temporal, bones. 

 These completely shut off this space, except for the foramina. 



In my embryo there do not appear to be any of the nodules 

 corresponding to the three Uestknorpeln of Voit. The space 

 corresponding to the above cavities is filled with loose connective 

 tissue containing vessels and nerves. The dura has not condensed, 

 is loose, and spreads outward and upward from the level of 

 the upper part of the pituitary body. Thus the primitive 

 cranial floor and side-wall of this region is not represented in 

 my model. There is, however, what may be a rudiment of 

 the cartilaginous secondary cranial floor — the floor of the cavum 

 epiptericum, viz., the small nodule which T have called the carti- 

 lago supracochleare. Voit considers the ahcochlearis a part of 

 this floor, which dorsally is directly continuous with the planum 

 supracochleare; this being so it follows that, if the cartilago 

 supracochleare be regarded as a rudiment of the commissura 

 ahcochlearis it is then a rudiment of the cartilaginous floor 

 of the cavum epiptericum, or, more accurately, the cavum 

 supracochleare. 



Regio ethmoidalis 



The ethmoidal region is the most ventral of the primary 

 divisions of the chondrocranium. With the orbitotemporal 

 region it is directly continuous at three points, as we have seen; 

 medially the septum nasi passes directly backward into the sep- 

 tum interorbitale, and laterally the upper portion of the lateral 

 wall of the ectethmoid is united, on each side, with the spheno- 

 ethmoidal cartilage through the sphenoethmoidal commissure 

 and the line of bridges of cartilage dorsal to the latter. 



Architecturally considered the principal elements entering 

 into the construction of the ethmoidal region are those going to 

 form the nasal capsule, but this region also includes certain 

 accessory cartilages, of which there are, in relation to the septum 

 the anterior and superior paraseptals; in relation to the lateral 

 wall (intracapsular) the cartilago meatus medii, and (extracap- 

 sular) the paraethmoidal and paranasal cartilages. 



