318 



CHARLES CLIFFORD MACKLIN 



It will be seen that a considerable interval, occurs between the 

 last two stages in this list, and with a view towards lessening 

 it I undertook, at the suggestion of Professor McMurrich, the 

 study of the skull of a fetus of 40 mm., crown-rump measure- 

 ment, which would correspond, according to Mall's formula 

 (Mall '06, p. 439), to an age of 63 days. The entire head of the 

 fetus had been cut into serial sections in the frontal plane, the 

 sections being 20 micra in thickness and stained with haemalum 

 followed by erythrosin. From these sections the entire skull, 

 together with the membrane bones and upper two visceral arches, 

 was reconstructed by the wax plate method at an enlargement 

 of 30 diameters, and, to facilitate the study of the nasal and otic 

 capsules, separate models were made, at the same magnification, 

 of the mesethmoid, ectethmoid, right otic capsule and the anlage 

 of the right osseous labyrinth. Drawings were made of every 

 other section by the use of Edinger's "Drawing and projection 

 apparatus," only that tissue being included as cartilage which 

 presented a homogeneous, blue ground-substance and could 

 be clearly differentiated from its surroundings, i.e., the tissue 

 which Levi ('00) has described under the terms 'alteren Vor- 

 knorpel' or older precartilage, and "Knorpel"" or cartilage. The 

 earlier chondrogenic tissue of which there was very little at this 

 stage, was disregarded. 



The sections were not exactly in the frontal plane and to elimi- 

 nate any lateral distortion in the models the amount of obliq- 



